Find the length of the missing side of the triangle

It is a right triangle, so we can use pythagorean theorem which states

a^2 + b^2 = c^2

Leg^2 + Leg^2 = Hypotenuse^2

9^2 + x^2 = 15^2

81 + x^2 = 225

x^2 = 144

x=12

It is 6% because if you subtract 69-58=6 so 6% is the answer to your question.