This is a question that can be solved with Pythagorean Theorem since it is a right triangle. The longest side, 29, is the hypotenuse and the sides 21 and x are the legs. So, the Pythagorean Theorem states,
Where,
c is the Hypotenuse, a and b are the legs. Putting the respective values gives us,
So, 20 is the side length of x.
ANSWER: 20