Find the Critical Number(s), If Any, of the Function $h(u)=\frac{7 u}{u^{2}+36}$

Multiple Choice

Find the critical number(s) , if any, of the function $h(u) =\frac{7 u}{u^{2}+36}$ .

A) $\frac{7}{36}$
B) $\pm 6$
C) $\frac{7}{6}$
D) None of these