Solve by Substitution y=3x-4 -3y=-9x+12

$y = 3 x - 4$ $- 3 y = - 9 x + 12$

Step 1

Replace all occurrences of $y$ with $3 x - 4$ in each equation.

Replace all occurrences of $y$ in $- 3 y = - 9 x + 12$ with $3 x - 4$ .

$- 3 (3 x - 4) = - 9 x + 12$

$y = 3 x - 4$

Simplify the left side.

Simplify $- 3 (3 x - 4)$ .

Apply the distributive property.

$- 3 (3 x) - 3 \cdot - 4 = - 9 x + 12$

$y = 3 x - 4$

Multiply.

Multiply $3$ by $- 3$ .

$- 9 x - 3 \cdot - 4 = - 9 x + 12$

$y = 3 x - 4$

Multiply $- 3$ by $- 4$ .

$- 9 x + 12 = - 9 x + 12$

$y = 3 x - 4$

$- 9 x + 12 = - 9 x + 12$

$y = 3 x - 4$

$- 9 x + 12 = - 9 x + 12$

$y = 3 x - 4$

$- 9 x + 12 = - 9 x + 12$

$y = 3 x - 4$

$- 9 x + 12 = - 9 x + 12$

$y = 3 x - 4$

Step 2

Remove any equations from the system that are always true.

$y = 3 x - 4$

Step 3

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