Giving marbles across does not change the total (60 + 9 = 69). In the end Bob = twice Nick, so Nick = 1 unit, Bob = 2 units, 3 units in all.

Nick after1Bob after11total stays 60 + 9 = 69

Plain numbers are given; italic underlined numbers are worked out.

  1. Total → 60 + 9 = 69 (unchanged)
  2. 3 units → 69
  3. 1 unit (Nick after) → 69 ÷ 3 = 23; Bob after = 46
  4. Bob gives → 60 − 46 = 14

Bob must give Nick 14 marbles.

Check: Bob 46, Nick 23, 46 = 2 × 23, total 69. ✓