What is the length of the side of a right triangle that has a hypotenuse that is 15 mm and a side that is 9 mm? a.12 mm b.15 mm c.27 mm d.45 mm

A. 12 mm

The Pythagorean Theorem states that a^2 + b^2 = c^2 with a and b being lengths of legs and c being the length of a hypotenuse. So we can use our givens to solve for the remaining leg. 

9^2 + b^2 = 15^2
81 + b^2 = 225
b^2 = 144
b = 12