Answer:
(-18,9)
Step-by-step explanation (work shown in picture attached):
1) The first step in solving by substitution is to isolate the y-term in one of the equations if it is not already isolated. Isolate y in the first equation by dividing both sides by -2. This leaves us with the equation
2) Now, substitute
for the y in the second equation. Simplify and isolate x. (You can multiply everything by -2 to get rid of the fraction.) This leaves us with x = -18.
3) We've found the x-value of the solution, -18. Now, substitute -18 for x back into one of the original equations (I chose the first one because it was simple) and isolate y. This gives us y = 9. Thus, in point form, the answer is (-18,9).