help me with my math homework, is about a really weird equation?

[еl©ë]

find each of the following.
a. ƒ(x-2) if ƒ(x)=-4x
b. 3+ƒ(x+4) if ƒ(x)=2x

 

[Alucard]

plug in x-2 for x, f(x)=-4x+8
plug in x+4 for x, f(x)=2x+8, then add 3, 2x+11