The correct answer is 12. Hope this helps.
Looks like the integral is supposed to read

The same integral in the required order is

I’m learning this as well. It’s really easy.
The zeros or roots are x= 6, -3, -5.
-125g ^2 that’s what I got solving for it
Complementary means sum = 90, so 90-57 to get the other angle at 23 degrees
Supplementary means sum = 180, so 180-52 to get the other angle at 128 degrees