Answer: x = 12
The triangles are similar, so the corresponding sides on each triangle can be turned into ratios
(4x + 12)/(15) = (32)/(8) (ratios)
(8(4x + 12))/120 = (32)(15)/120 (multiple denominators to make them equal)
(32x + 96)/120 = 480/120 (distribute)
32x + 96 = 480 (forget the denominators since they’re the same now)
32x = 384 (subtract 96 from both sides)
x = 12 (divide both sides by 32