Answer:
12 in.
Explanation:
You have to use the Pythagorean theorem for this problem. Since we are solving for DE, we do:
5 squared + b squared = 13 squared
25 + b squared = 169
Isolate the b:
25 - 25 + b squared = 169 - 25
b squared = 144
Find the square root of 144 = 12
(The formula for the Pyathagorean theorem is a squared + b squared = c squared)