Because you can't solve for two variables at once, you can guess and trial/error.
You can also give x or y any value, and then solve for the opposite variable.
x = 0
y = -36
for example. There are more solutions.
y + 8 = -4(x+7)
-36 + 8 = -4(0+7)
-28 = 0 - 28
-28 = -28
