$\displaystyle (f(a+h)-f(a))/h$ where a = 5 and h = 1
Was this all the question asked? It seems to simple. Did the question by chance ask to calculate:
$\displaystyle \lim_{h \to 1} \frac{f(a+h)-f(a)}{h}$
with $\displaystyle a = 5$
??
Or did it indeed ask exactly as you had said, to simply calculate the value of the function?
(I know, this may seem like an unneccesary post, but I am just trying to make sure it wasn't the limit that they were asking you to calculate, since something of the form:
$\displaystyle \frac{f(a+h)-f(a)}{h}$
is used in problems with limits very, very, very often. And since this question is in the calculus thread area.)