900 - (48*7:6 - 4*5) = 900 - ( 336 :6 - 20) = 900 - (56 - 20) = 900 - 36 = 864
900 - (48*7:6 - 4)*5 = 900 - ( 56 - 4)*5 = 900 - 52*5 = 900 - 260 = 640
(900 - 48*7):6 - 4*5 = (900 - 336):6 - 20 = 564:6 -20 = 94 - 20 = 74
900 - 48*7:(6-4)*5 = 900 - 336: 2*5 = 900 - 336:10 = 900 - 33,6 = 866,4