You have got to start reading and understanding your class notes and textbook! Many of the questions you are posting are done using basic definitions and formulae. MHF is not a service for doing all your homework.

This question is nothing more than applying a basic formula:

Cov(X, Y + Z) = Cov(X, Y) + Cov(X, Z).

See here: Covariance - Wikipedia, the free encyclopedia