This is a right triangle and the hypotenuse is what we are looking for, c. The formula to find the length of the hypotenuse is Pythagroean's Theorem, or

. Let's let a = 8 and b = 12. Filling in the formula then we have

and

and

. c then is equal to

. 208 is not a perfect square, so if you simplify it and use the decimal form, it is 14.422, but if you leave it in radical form it simplifies to

. I don't see that as one of your choices, but that's the answer.