Ответ:1. 3 1/2 - 5 3/4 = 7/2 - 23/4 = 14/4 - 23/4 = -9/4.2. 2 1/4 - 3 = 9/4 - 12/4 = -3/4.3. 9 + (-9/4) : (-3/4) = 9 + 3 = 12.