7 целых 26/39 = (7 * 39 + 26) / 39 = 283/39

4 целых 14/21 = (4 * 21 + 14) / 21 = 98/21 = 4 целых 10/21

12 целых 4/6 = (12 * 6 + 4) / 6 = 76/6 = 12 целых 4/6 = 12 целых 2/3