Пошаговое объяснение:

1) 4/15 * 25/28 = 1/3 * 5/7 = 5/21

2) 6 * 14/36 = 1 * 14/6 = 14/6 = 7/3 = 2 1/3

3) 14/25 : 7/10 = 14/25 * 10/7 = 2/5 * 2/1 = 4/5

4) 16 : 8/13 = 16 * 13/8 = 2 * 13/1 = 26/1 = 26