Ответ:

  1. 13 − 7 = 6; 6 + 6 = 12; 12 − 8 = 4.
  2. 5 + 8 = 13; 13 − 4 = 9; 9 + 3 = 12.
  3. 16 − 8 = 8; 8 + 4 = 12; 12 − 9 = 3.
  4. 9 + 6 = 15; 15 − 8 = 7; 7 + 7 = 14.

Ответ: 6, 12, 4; 13, 9, 12; 8, 12, 3; 15, 7, 14.