Most likely the figure is a triangle. Thus, the sum of the angles is 180 and the third angle is:
180 - 62 - 39 = 79 <-- This will be angle c
We then use the law of sines to find the length C.
a/sin A = c/sin C = b/sin B
length C = (15/sin39) (sin 79)
length C = 23.40