Question

f(x+h) = Given: F(x) = 2x + 3, find and simplify.

Answer 1

Something's not quite write about your problem statement.  I think you meant the following:

Given F(x) = 2x + 3, find and simplify F(x+h).

F(x+h) = 2(x+h) + 3 = 2x + 2h + 3.  

I'd say you could come out equally well by leaving your result as

F(x+h) = 2(x+h) + 3  

or by removing the parentheses:   2x + 2h + 3