Answer
$4$ units
Work Step by Step
For a right triangle, we can apply the Pythagorean theorem, that states:
$c^2=a^2+b^2$, where $c$ is the length of the hypotenuse; $a$ and $b$ are the lengths of the legs,
Here, by substituting in the values given:
$5^2=3^2+b^2$
$b^2=25-9=16$
$b=\pm4$
Since a length cannot be negative, then $b=4$.
