To find the missing side length of each triangle, use the pythagorean theorem. The theorem is where a, b, and c are all side lengths of the triangle. a is the smallest lef and b is the other leg while c is always the hypotenuse or longest side.
In d, you'll use it twice to find the missing measure. First use it when a = 12 and b = 20. So you'll have:
Repeat the same process using a = 9 and c = 23.32. Then solve for the b value.