If $f$ and $g$ are the functions whose graphs are shown, let $u(x)=f(g(x)), v(x)=g(f(x))$, and $w(x)=g(g(x))$.
Find each of the following derivatives, if they exist. If it does not exist, enter "dne" (without the quotes) below.

(a) $u'(3) =$
(b) $v'(3) =$
(c) $w'(3) =$