Пошаговое объяснение:

1) 4 : 3/5 = 4 * 5/3 = 20/3 = 20 : 3

2) 4/9 : 5/9 = 4/9 * 9/5 = 4/5 = 4 : 5

3) 1,8 : 0,4 = 18/10 : 4/10 = 18/10 * 10/4 = 9/1 * 1/2 = 9/2 = 9 : 2

4) 3/14 : 1 2/7 = 3/14 : 9/7 = 3/14 * 7/9 = 1/2 * 1/3 = 1/6 = 1 : 6