Answer
$C\approx4\pi\sqrt {82}\approx113.79$.
Work Step by Step
$C\approx 2\pi \sqrt {\frac{a^{2}+b^{2}}{2}}=2\pi\sqrt {\frac{20^{2}+16^{2}}{2}}$
$=2\pi\sqrt {\frac{400+256}{2}}=2\pi\sqrt {328}$
$=2\pi \sqrt {4\cdot82}=2\pi\sqrt {4}\cdot \sqrt {82}$
$=2\pi (2)\sqrt {82}=4\pi\sqrt {82}$
$C\approx4\pi\sqrt {82}\approx113.79$.
