Answer
120
Work Step by Step
$r(x)=f(g(h(x)))$ ___(1)
Differentiate (1) with respect to $x$ by using chain rule
$r^{'}(x)=f^{'}(g(h(x)))\cdot g^{'}(h(x))\cdot h^{'}(x)$
$r^{'}(1)=f^{'}(g(h(1)))\cdot g^{'}(h(1))\cdot h^{'}(1)$
Using given data $h(1)=2, \; g(2)=3\;, h^{'}(1)=4,\;g^{'}(2)=5,\;f^{'}(3)=6$
$r^{'}(1)=f^{'}(g(2))\cdot g^{'}(2)\cdot 4$
$r^{'}(1)=f^{'}(3)\cdot 5\cdot 4$
$r^{'}(1)=6\cdot 5\cdot 4$
$r^{'}(1)=120$
