1) (12*35*72)/(25*54*28) = (12*7*72)/(5*54*28) = (12*72)/(5*54*4)= (3*72)/(5*54) = (3*8)/(5*6) = (8)/(5*2) = 4/5;
2) (62*5 + 62+15) / (31*35 + 31*15) = (62*(5 + 15)) / (31*(35 - 15)) = (62*20)/(31*20) = 62/31 = 2;
3) (5a+6a+7a)/(24a - 15a) = 18a / 9a = 2;