Question

what is the perimeter? if necessary, round to the nearest tenth.
$square$ millimeters
8 mm
7 mm
b

Explanation:

Step1: Solve for side $b$ via Pythagoras

$$b = \sqrt{8^2 - 7^2} = \sqrt{64 - 49} = \sqrt{15} \approx 3.9$$

Step2: Sum all sides for perimeter

$$\text{Perimeter} = 7 + 8 + 3.9$$

Answer:

18.9 millimeters