The equation for Pythagorean theorem is
a^2 + b^2 = c^2
c = the hypotenuse of a right angle, the longest sides
a, and b is the shorter sides of the right angle
Since we have the hypotenuse, and one number for the other side, cut the other side (6) in half because of how a area of a triangle is based off the equation, h x b divided by 2 = A
Plug it into the equation above:
3^2 + b^2 = 8^2
9 + b^2 = 64
b^2 = 55
b = √55
D. x = √55 is your answer