You will get a brain list if the answer is right.

15

Step-by-step 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

the answer is:   y = 1/3x - 2