Answer:
since they are alternate exteriors, we put a equal sign
2x+78=5x+15
next we subtract 78 on both sides
2x+78-78=5x+15-78
2x=5x-63
then we subtract 5x on both sides
2x-5x=5x-5x-63
-3x=-63
after that we divide -3 on both sides
-3x/-3=-63/-3
and the answer is
x=21
Explanation: