How does this substitution rule in calculus work?

Step-by-step explanation:

Using the u-substitution rule makes it easier to read and work with composite functions, i.e. (f(g(x)) by putting the variable u in place of the inner function, or g(x). You then multiply this by the derivative of u, also called du. Then, you place your original function in place of u and the derivatives, which gives you your answer.

55 degrees because 55+55=110 degrees