Hey there!!
We will have to use the pythogorean theorem in order to solve this.
The measure of the legs = 5 and 12
Measure of hypotenuse = x
Hence,
... x² = 5² + 12²
... x² = 25 + 144
... x² = 169
... x = √169
... x = 13
The answer is 13
Hope my answer helps!!