7/2 : ((53/12 - 85/24) * 4/7 + (55/18 - 31/12) * 27/17) = 7/2 : ((106 - 85)/24 * 4/7 + (110 - 93)/36 * 27/17) = 7/2 * (1/2 + 3/4) = 7/2 : 5/4 = 28/10 = 2,8