7 1/7*15 3/4*28,5:4,2*12,5*10 5/9

Решаем пример по действиям:

1) 7 1/7 * 15 3/4 = (7 * 7 + 1) / 7 * (15 * 4 + 3) / 4 = 50/7 * 63/4 = (50 * 63) / (7 * 4) = (25 * 9) / 2 = 225/2;

2) 225/2 * 28,5 = 225/2 * 285/10 = (225 * 285) / (2 * 10) = (45 * 285) / 4 = 12825/4;

3) 4,2 * 12,5 = 42/10 * 125/10 = (21 * 5) / 2 = 105/2;

4) 105/2 * 10 5/9 = 105/2 * (10 * 9 + 5) / 9 = 105/2 * 95/9 = (105 * 95) / (2 * 9) = (35 * 95) / (2 * 3) = 3325/6;

5) 12825/4 : 3325/6 = 12825/4 * 6/3325 = (12825 * 6) / (4 * 3325) = (27 * 3) / (2 * 7) = 81/14;

Ответ: 81/14.