The sum of the 3 inside angles need to equal 180.
You know 2 of the angles: 90 and 39
The third angle is 180 - 90 - 39 = 51 degrees.
Side a is given as 24
Side B = tan(39) = b/24 = 19.43 (round as needed)
Side C = cos(39) = 24/c = 30.88 (round as needed)
