What have you done ?
First : f(2x)= ?
No. f(x) is a notation that says "the function operated on the value x". Here we are told , which says that whatever value you put in, is what you will raise 3 to the power of, and then add 2 to. So if instead we put in 2x we get f(2x). If the same function operates on 2x (so this is what we raise 3 to the power of and then add 2 to), what will we get?