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