a) 306/14 * 18/85 * 56/3 = 432/5 = (430+2)/5 = 86 si 2/5
b) 68/15 : 26/25 : 17/3 = 68/15 x 25/26 x 3/17 = 10/13
c) 48/35 : 39/7 x 143/60 = 48/35 x 7/39 x 143/60 = 44/75
d) 111/8 - 39/12 -7/4 = 111/8 - 13/4 - 7/4 = 111/8 - 26/8 - 14/8 = 71/8 = (64+7)/8 = 8 si 7/8