#### Answer

4

#### Work Step by Step

The Pythagorean Theorem says that $(leg_{1}) ^{2}$+$(leg_{2})^{2}$=$hypotenuse^{2}$.
This formula is more commonly referred to as $a^{2}$+$b^{2}$=$c^{2}$
You are given the length of one leg as 3 and the length of the hypotenuse as 5. Substitute 3 in for a and 5 in for c.
$a^{2}$+$b^{2}$=$c^{2}$
$3^{2}$+$b^{2}$=$5^{2}$
9+$b^{2}$=25
Subtract 9 from both sides.
$b^{2}$=16
Take the square root of both sides to find the length of the missing side.
b=4