Find integral from a known integral 
The correct answer is $7$. I figured out that if you substitute the inner argument of the second function, the end points become the same but flipped. That means we can just negate the integral and get the same endpoints. This is where I am now stuck. How do I get to the result with that knowledge?

Substituting in the second argument  you get
$$-\frac{1}{8}\int_7^{-145}f(y)dy=\frac{1}{8}\int_{-145}^{7}f(y)dy=\frac{56}{8}=7$$
