Question

Solve using the substitution method.
18x + 6y = 78
12x + 54y = -48

Answer 1

first simplify the equations
the first is 3x + y =13, the second 2x + 9y = -8.

solve the first for y to get y = 13-3x

plug y into the second equation to get
2x + 9(13-3x) = -8
2x + 117 -27x = -8
-25x = -185
x = 185/25 == 37/5 == 7.4

then plug x into the equation we solved for y to get
y = 13-3(37/5)
y = 13 - 111/5
y = -9.2

Answer 2

I built off of yours so thank you, but I'm not sure how you got the -185? I got -125 so x=-5.

Answer 3

Final Answer:
18x+6y=78 3x+y=13
12x+54y=-48 2x+9y=-8

y=-3x+13
2x+9y=-8

2x+9(-3x+13)=-8
2x+(-27x)+117=-8
25x=-125
x=-5

3x+y=13
3(-5)+y=13
-15+y=13
y=28

(-5,28)