Solve by substitution x-y=12 x+y=18

X = y + 12. You then substitute or plug in that from the first equation into the second equation. You get (y+12)+y=18, then you simplify to get your y value. In this case y = 3. The you can plug your y value into either equation. (x+3=18) or (x-3=12) or (x=3+12) either way you get x=15 and y=3.

f(x) = - 3x + 4

Step-by-step explanation:

9x + 3y = 12

3y = - 9x + 12

y = - 3x + 12

f(x) = - 3x + 12

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