This question is pretty easy. All you need to do is use the pythagorean theorem. A^2+B^2=C^2
(20)^2+(15)^2=C^2
400+225=C^2
625=C^2
To get the C alone you need to do the opposite of squaring something which is taking the square root of something.
So, this means that the answer is C=25
Hope this helps!
