Answer:
12cm
Step-by-step explanation:
pythagorean theorem!
a^2 + b^2 = c^2
7^2 + b^2 = 13^2
49 + b^2 = 169
49 - 49 + b^2 = 169 - 49 (whatever you do to one side, you do to the other side)
b^2 = 147 (square root)
= 12cm
