Help..? Pleaseee , it has to do with the Pythagorean Theorem. But I have no idea how to do it

Pythagorean Theorem is

a ²+ b ² = c ²

a and b are the shorter sides, while c is the hypotenuse, or longest side. Let’s say the side we are looking for is “b”.

Let’s first rearrange the equation, then sub in.

a ²+ b ² = c ²
b ² = c ²- a ²
b = √ (c ²- a ²)
b = √(17 ²- 15 ²)
b = √(289-225)
b = √ 64
b = 8