HELP ME! I BEG YOU

12

Step-by-step explanation:

Using the pythagorean theorem we have DE^2 + 5^2 = 13^2

DE^2 = 169 - 25 = 144

DE  = sqrt144 = 12

Or, you could just remember the triangle 5-12-13, as it is pretty common, along with 3-4-5, 7-24-25