#### Answer

$c=5$

#### Work Step by Step

According to the Pythagorean Theorem, if $a$ and $b$ are the lengths of the shorter sides of a right triangle and $c$ is the length of the longest side, then $a^{2}+b^{2}=c^{2}$.
Therefore, $3^{2}+4^{2}=c^{2}$.
$9+16=c^{2}$
$25=c^{2}$
Take the square root of both sides.
$\sqrt 25=c=5$ (where we know that $c$ must be positive, since it is a length)