#### Answer

sum

#### Work Step by Step

RECALL:
$(f+g)(x) = f(x) + g(x)$. This means the value of $(f+g)(x)$ is equal to the sum of the values of $f(x)$ and $g(x)$.
Thus, in the graph of $(f+g)(x)$, the height of $(f+g)(a)$ is equal to the sum of the heights of $f(a)$ and $g(a)$.
Therefore, the answer is: sum