How can you use addition and subtraction to put together and separate measures of an angle and its parts?

We can use addition and subtraction to put together and separate measures of an angle and its parts by looking for the complementary or the supplementary angles. 

For example, What is the other angle in a complementary angle in which one of the angles is 45 degrees. This is how should be answered. Ccomplementary angles are two angles that forms a total of 90 degrees.
90 = A + B
90 = 45 + B
B = 90 - 45
B = 45