1)
1 4/9 - 7/12 = 13/9 - 7/12 = (52-21)/36=31/36 - разница
1 4/9 + 31/36 = 13/9 + 31/36 = (52+31)/36=83/36= 2 целых 11/36
Ответ. С=2 целых 11/36
2)
6 5/27 - 3 7/18 = 3 (10-21)/54 = 2 (64-21)/54 = 2 43/54
3 7/18 - 2 43/54 = 1 (21-43)/54 = (75-43)/54 = 32/54 = 16/27
Ответ. С=16/27