#### Answer

$c = 5$

#### Work Step by Step

We can find the value of $c$:
$c^2 = a^2+b^2$
$c^2 = (3)^2+(4)^2$
$c^2 = 9+16$
$c^2 = 25$
$c = \pm \sqrt{25}$
$c = -\sqrt{25}~~$ or $~~c = \sqrt{25}$
$c = -5~~$ or $~~c = 5$
Since the value of $c$ must be positive, $c = 5$