Answer
Let $f(x)=2x+1$ and $g(x)=x-4$ for this problem.
$f(x)=2x+1$
$f(2)=2*2+1$
$f(2)=4+1$
$f(2)=5$
$g(x)=x-4$
$g(2)=2-4$
$g(2)=-2$
Work Step by Step
One way to find $(f+g)(x)$ is to add the functions together.
$(f+g)(x) = (2x+1) + (x-4) = 2x+1+x-4 = 3x-3$
Another way to find $(f+g)(x)$ is to take the composition of the two functions.
$f(g(x)) = f(x-4) = 2(x-4)+1 = 2x-8+1 = 2x-7$.