SOLUTION STEPS:
  1. Total money = $15 + $11 = $26. Does not change.
  2. After: B = 1 unit, A = 1 unit + 20. 2 units + 20 = 26, so 2 units = 6, 1 unit = 3.
  3. Move $11 - $3 = $8 from B to A.