Answer:
b=8
Explanation:
This is a right triangle, as we can see from the box in the corner.
We can use Pythagorean theorem to find the unknown side
a^2 +b^2 = c^2
where a and b are the legs and c is the hypotenuse
15^2 +b^2 = 17^2
225 + b^2 =289
Subtract 225 from each side
225-225 + b^2 = 289-225
b^2 =64
Take the square root of each side
sqrt(b^2) = sqrt(64)
b = 8