A)13/17 * 8/9 = (13*8)/(17*9) = 104/153
4/17 * 8/9 = (4*8)/(17*9) = 32/153
104/153+32/153 = (103+32)/153 = 135/153
11/16 + 3/8 = 11/16 + 6/16 = 17/16
17/16 * 135/153 = (17*135)/(16*153) = 15/16
b)3/4-15/16=12/16-15/16= -3/16
что значит 1-3 2/7 я не знаю