geometry
posted by lane .
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.