Section 9.1-9.5: Combining Functions
Combining Functions, addition, subtraction, multiplication, division AND composition
For video explanation look at
https://www.khanacademy.org/math/algebra/algebra-functions/eval-function-expressions/v/sum-of-functions
and various other videos in that location.
or
http://patrickjmt.com/functions-adding-and-subtracting/ or http://patrickjmt.com/functions-multiplying-and-dividing/ or http://patrickjmt.com/composition-of-functions/