What is the length of the hypotenuse of a 45°-45°-90° triangle
with leg length 5V3?

5

Step-by-step explanation:

The easiest way to do this problem is to know that the hypotenuse of a 45-45-90 triangle is equal to times the length of a leg.  

So, in your problem the hypotenuse = (5) = 5.   Another way to solve the problem is to use the Pythagorean theorem, but that is a longer way to solve it.

b, i believe, but not sure.