Answer:
15
Explanation:
We know according to the figure that 9^2+12^2 = z^2,
as a result, we know that z^2 = 225
and z = 15
Another method is to recognize that this figure is similar to a 3-4-5 triangle. According to the converse of the Hypotenuse-Leg theorem, we get that the third length of the triangle is 15