Right triangle ABC is similar to triangle XYZ, because angle B is congruent to angle Y. If side AB equals 15 inches, side BC equals 45 inches, and side YZ equals 9 inches, then what is the length of side XY?

XY/AB = YZ/BC,

XY/15 = 9/45,
Multiply both sides by 15:
XY = 135/45 = 3.

To find the length of side XY, we can set up a proportion using the corresponding sides of the similar triangles.

Since triangle ABC is similar to triangle XYZ, we can write the following proportion:

AB/XY = BC/YZ

Substituting the given values:

15/XY = 45/9

To solve for XY, we can cross multiply:

15 * 9 = 45 * XY

135 = 45 * XY

Now, we can solve for XY by dividing both sides of the equation by 45:

XY = 135/45

Simplifying:

XY = 3

Therefore, the length of side XY is 3 inches.