Ответ:а) 5/9 - 7/18 = 10/18 - 7/18 = 3/18 = 1/6.б) 4/5 - 5/8 = 32/40 - 25/40 = 7/40.в) 11/16 - 5/12 = 33/48 - 20/48 = 13/48.г) 8/21 - 4/35 = 40/105 - 12/105 = 28/105 = 4/15.