Since it is a right triangle, you can use the Pythagorean Theorem to find the length of the missing side.
a^2 + b^2 = c^2
(a and b are the legs, c is the hypotenuse)
In this triangle, a=21 and c=25. Find b.
21^2 + b^2 = 25^2
441 + b^2 = 625
b^2 = 184
b = 13.6
