Solve by Substitution 9a+3b=30 , 8a+4b=28

$9 a + 3 b = 30$ , $8 a + 4 b = 28$

Solve for $a$ in the first equation.

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Subtract $3 b$ from both sides of the equation.

$9 a = 30 - 3 b$

$8 a + 4 b = 28$

Divide each term by $9$ and simplify.

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Divide each term in $9 a = 30 - 3 b$ by $9$ .

$\frac{9 a}{9} = \frac{30}{9} + \frac{- 3 b}{9}$

$8 a + 4 b = 28$

Cancel the common factor of $9$ .

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Cancel the common factor.

$\frac{9 a}{9} = \frac{30}{9} + \frac{- 3 b}{9}$

$8 a + 4 b = 28$

Divide $a$ by $1$ .

$a = \frac{30}{9} + \frac{- 3 b}{9}$

$8 a + 4 b = 28$

$a = \frac{30}{9} + \frac{- 3 b}{9}$

$8 a + 4 b = 28$

Simplify each term.

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Cancel the common factor of $30$ and $9$ .

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Factor $3$ out of $30$ .

$a = \frac{3 (10)}{9} + \frac{- 3 b}{9}$

$8 a + 4 b = 28$

Cancel the common factors.

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Factor $3$ out of $9$ .

$a = \frac{3 \cdot 10}{3 \cdot 3} + \frac{- 3 b}{9}$

$8 a + 4 b = 28$

Cancel the common factor.

$a = \frac{3 \cdot 10}{3 \cdot 3} + \frac{- 3 b}{9}$

$8 a + 4 b = 28$

Rewrite the expression.

$a = \frac{10}{3} + \frac{- 3 b}{9}$

$8 a + 4 b = 28$

$a = \frac{10}{3} + \frac{- 3 b}{9}$

$8 a + 4 b = 28$

$a = \frac{10}{3} + \frac{- 3 b}{9}$

$8 a + 4 b = 28$

Cancel the common factor of $- 3$ and $9$ .

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Factor $3$ out of $- 3 b$ .

$a = \frac{10}{3} + \frac{3 (- b)}{9}$

$8 a + 4 b = 28$

Cancel the common factors.

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Factor $3$ out of $9$ .

$a = \frac{10}{3} + \frac{3 (- b)}{3 (3)}$

$8 a + 4 b = 28$

Cancel the common factor.

$a = \frac{10}{3} + \frac{3 (- b)}{3 \cdot 3}$

$8 a + 4 b = 28$

Rewrite the expression.

$a = \frac{10}{3} + \frac{- b}{3}$

$8 a + 4 b = 28$

$a = \frac{10}{3} + \frac{- b}{3}$

$8 a + 4 b = 28$

$a = \frac{10}{3} + \frac{- b}{3}$

$8 a + 4 b = 28$

Move the negative in front of the fraction.

$a = \frac{10}{3} - \frac{b}{3}$

$8 a + 4 b = 28$

$a = \frac{10}{3} - \frac{b}{3}$

$8 a + 4 b = 28$

$a = \frac{10}{3} - \frac{b}{3}$

$8 a + 4 b = 28$

$a = \frac{10}{3} - \frac{b}{3}$

$8 a + 4 b = 28$

Replace all occurrences of $a$ with $\frac{10}{3} - \frac{b}{3}$ in each equation.

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Replace all occurrences of $a$ in $8 a + 4 b = 28$ with $\frac{10}{3} - \frac{b}{3}$ .

$8 (\frac{10}{3} - \frac{b}{3}) + 4 b = 28$

$a = \frac{10}{3} - \frac{b}{3}$

Simplify $8 (\frac{10}{3} - \frac{b}{3}) + 4 b$ .

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Simplify each term.

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Apply the distributive property.

$8 (\frac{10}{3}) + 8 (- \frac{b}{3}) + 4 b = 28$

$a = \frac{10}{3} - \frac{b}{3}$

Multiply $8 (\frac{10}{3})$ .

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Combine $8$ and $\frac{10}{3}$ .

$\frac{8 \cdot 10}{3} + 8 (- \frac{b}{3}) + 4 b = 28$

$a = \frac{10}{3} - \frac{b}{3}$

Multiply $8$ by $10$ .

$\frac{80}{3} + 8 (- \frac{b}{3}) + 4 b = 28$

$a = \frac{10}{3} - \frac{b}{3}$

$\frac{80}{3} + 8 (- \frac{b}{3}) + 4 b = 28$

$a = \frac{10}{3} - \frac{b}{3}$

Multiply $8 (- \frac{b}{3})$ .

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Multiply $- 1$ by $8$ .

$\frac{80}{3} - 8 \frac{b}{3} + 4 b = 28$

$a = \frac{10}{3} - \frac{b}{3}$

Combine $- 8$ and $\frac{b}{3}$ .

$\frac{80}{3} + \frac{- 8 b}{3} + 4 b = 28$

$a = \frac{10}{3} - \frac{b}{3}$

$\frac{80}{3} + \frac{- 8 b}{3} + 4 b = 28$

$a = \frac{10}{3} - \frac{b}{3}$

Move the negative in front of the fraction.

$\frac{80}{3} - \frac{8 b}{3} + 4 b = 28$

$a = \frac{10}{3} - \frac{b}{3}$

$\frac{80}{3} - \frac{8 b}{3} + 4 b = 28$

$a = \frac{10}{3} - \frac{b}{3}$

To write $4 b$ as a fraction with a common denominator, multiply by $\frac{3}{3}$ .

$\frac{80}{3} - \frac{8 b}{3} + 4 b \cdot \frac{3}{3} = 28$

$a = \frac{10}{3} - \frac{b}{3}$

Combine $4 b$ and $\frac{3}{3}$ .

$\frac{80}{3} - \frac{8 b}{3} + \frac{4 b \cdot 3}{3} = 28$

$a = \frac{10}{3} - \frac{b}{3}$

Combine the numerators over the common denominator.

$\frac{80}{3} + \frac{- 8 b + 4 b \cdot 3}{3} = 28$

$a = \frac{10}{3} - \frac{b}{3}$

Combine the numerators over the common denominator.

$\frac{80 - 8 b + 4 b \cdot 3}{3} = 28$

$a = \frac{10}{3} - \frac{b}{3}$

Multiply $3$ by $4$ .

$\frac{80 - 8 b + 12 b}{3} = 28$

$a = \frac{10}{3} - \frac{b}{3}$

Add $- 8 b$ and $12 b$ .

$\frac{80 + 4 b}{3} = 28$

$a = \frac{10}{3} - \frac{b}{3}$

Factor $4$ out of $80 + 4 b$ .

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Factor $4$ out of $80$ .

$\frac{4 \cdot 20 + 4 b}{3} = 28$

$a = \frac{10}{3} - \frac{b}{3}$

Factor $4$ out of $4 \cdot 20 + 4 b$ .

$\frac{4 (20 + b)}{3} = 28$

$a = \frac{10}{3} - \frac{b}{3}$

$\frac{4 (20 + b)}{3} = 28$

$a = \frac{10}{3} - \frac{b}{3}$

$\frac{4 (20 + b)}{3} = 28$

$a = \frac{10}{3} - \frac{b}{3}$

$\frac{4 (20 + b)}{3} = 28$

$a = \frac{10}{3} - \frac{b}{3}$

Solve for $b$ in the first equation.

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Multiply both sides of the equation by $\frac{3}{4}$ .

$\frac{3}{4} \cdot \frac{4 (20 + b)}{3} = \frac{3}{4} \cdot 28$

$a = \frac{10}{3} - \frac{b}{3}$

Simplify both sides of the equation.

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Simplify $\frac{3}{4} \cdot \frac{4 (20 + b)}{3}$ .

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Cancel the common factor of $3$ .

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Cancel the common factor.

$\frac{3}{4} \cdot \frac{4 (20 + b)}{3} = \frac{3}{4} \cdot 28$

$a = \frac{10}{3} - \frac{b}{3}$

Rewrite the expression.

$\frac{1}{4} \cdot (4 (20 + b)) = \frac{3}{4} \cdot 28$

$a = \frac{10}{3} - \frac{b}{3}$

$\frac{1}{4} \cdot (4 (20 + b)) = \frac{3}{4} \cdot 28$

$a = \frac{10}{3} - \frac{b}{3}$

Cancel the common factor of $4$ .

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Cancel the common factor.

$\frac{1}{4} \cdot (4 (20 + b)) = \frac{3}{4} \cdot 28$

$a = \frac{10}{3} - \frac{b}{3}$

Rewrite the expression.

$20 + b = \frac{3}{4} \cdot 28$

$a = \frac{10}{3} - \frac{b}{3}$

$20 + b = \frac{3}{4} \cdot 28$

$a = \frac{10}{3} - \frac{b}{3}$

$20 + b = \frac{3}{4} \cdot 28$

$a = \frac{10}{3} - \frac{b}{3}$

Simplify $\frac{3}{4} \cdot 28$ .

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Cancel the common factor of $4$ .

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Factor $4$ out of $28$ .

$20 + b = \frac{3}{4} \cdot (4 (7))$

$a = \frac{10}{3} - \frac{b}{3}$

Cancel the common factor.

$20 + b = \frac{3}{4} \cdot (4 \cdot 7)$

$a = \frac{10}{3} - \frac{b}{3}$

Rewrite the expression.

$20 + b = 3 \cdot 7$

$a = \frac{10}{3} - \frac{b}{3}$

$20 + b = 3 \cdot 7$

$a = \frac{10}{3} - \frac{b}{3}$

Multiply $3$ by $7$ .

$20 + b = 21$

$a = \frac{10}{3} - \frac{b}{3}$

$20 + b = 21$

$a = \frac{10}{3} - \frac{b}{3}$

$20 + b = 21$

$a = \frac{10}{3} - \frac{b}{3}$

Move all terms not containing $b$ to the right side of the equation.

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Subtract $20$ from both sides of the equation.

$b = 21 - 20$

$a = \frac{10}{3} - \frac{b}{3}$

Subtract $20$ from $21$ .

$b = 1$

$a = \frac{10}{3} - \frac{b}{3}$

$b = 1$

$a = \frac{10}{3} - \frac{b}{3}$

$b = 1$

$a = \frac{10}{3} - \frac{b}{3}$

Replace all occurrences of $b$ with $1$ in each equation.

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Replace all occurrences of $b$ in $a = \frac{10}{3} - \frac{b}{3}$ with $1$ .

$a = \frac{10}{3} - \frac{1}{3}$

$b = 1$

Simplify $\frac{10}{3} - \frac{1}{3}$ .

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Combine the numerators over the common denominator.

$a = \frac{10 - 1}{3}$

$b = 1$

Simplify the expression.

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Subtract $1$ from $10$ .

$a = \frac{9}{3}$

$b = 1$

Divide $9$ by $3$ .

$a = 3$

$b = 1$

$a = 3$

$b = 1$

$a = 3$

$b = 1$

$a = 3$

$b = 1$

List all of the solutions.

$a = 3, b = 1$

Solve by Substitution 9a+3b=30 , 8a+4b=28

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