Help with 11th grade Math question?(Link to problem)

Just studying for my TAKS test tommorow (that's my state-wide test btw).
I need help with problem #2 (how to break down the triangle, how to solve, and get the answer)
Thanks in advance!
:)

http://ritter.tea.state.tx.us/student.as…

Since the triangle is isosceles, you can say that the segments WZ and ZY are equal.
WY is 10 so WZ and ZY must each be 5.

Now that you have WZ and WX, you have two of three sides to a right triangle.

Use the pythagorean theorem to find the missing side length.
a^2 + b^2 = c^2
5^2 + b^2 = 13^2
b^2 = 169 - 25
b^2 = 144
b = 12


good luck on your test!