Answer:
(-3, -12)
Step-by-step explanation (work shown in attached picture):
1) First, since y is already isolated in the first equation, substitute that value of y into the other equation. So, substitute 4x for the y in x + y = -15 and solve for x. We find that x = -3.
2) Then, substitute that value for x back into any one of the equations. I chose to do it with the first equation. Substitute -3 for x in y = 4x, then solve for y this time. This gives us y = -12.
Since x = -3 and y = -12, the solution is (-3, -12).
