Answer:
Y = 12 cm
Explanation:
So you see the long side labeled as Z that will always be the C in Pythagorean theorem. The X and Y side can be put on A and B. It doesn't really matter which one.
5^2 + B^2 = 13^2
25 + B squared = 169
subtract 25
B squared = 144
Square root both sides
B = 12
B is the replacement of Y
Y = 12 cm