Answer: 3 times the square root of 5! (Or the square root of 45 if you don’t want to simplify)
Explanation:
First, you would need to use the Pythagorean Theorum, a^2 + b^2 = c^2, since it is a right triangle.
So in this case,
6^2 + 3^2 = c^2
This simplfys to:
36 + 9 = c^2
45 = c^2
Now you have to take out the square in the c. What you do to one side, you have to do to the other, so you have to put 45 in a square root. This simplies to 3 times the square root of 5.