7 4/9 + 3 3/4 = 67/9 + 15/4 = 403/ 36 = 11 7/36
5 3/4 + 2 1/6 = (5 + 2) + (3/4 + 1/6 ) = 7 11/12
7 3/5 -2 1/8 = 38/5 - 17/8 = 219/40 = 5 19/40
8 3/8 + 2 1/5 = (8 + 2) + (3/8 + 1/5) = 10 + 23/40 = 10 23/40
4 3/7 + 2 1/4 = (4+2) + (3/7 + 1/4) = 6 + 19/28 = 6 19/28