5) 2 2/5*5/6-3/4 * 1 2/3
6) 1 17/28*7/9+14/25*5/7

5)2/3

6)33/20

Вроде так,могу ошибаться

5) 2 2/5*5/6-3/4 * 1 2/3 = 12/5*5/6 - 3/4*5/3= 2-1 1/4 = 3/4

6) 1 17/28*7/9+14/25*5/7 =45/28*7/9 14/25*5/7 = 5/4+2/5 = 25/20 + 8/20 = 33/20 = 1 13/20