SOLUTION STEPS:
  - Add the known parts: 10 + 5 + 1/50 = 15 + 0.02 = 15.02.
  - Subtract from 15.12: 15.12 - 15.02 = 0.10 = 1/10.
  - 1/10 is NOT among A-C (5/10, 8/10, 3/10). Choose "None of the above".