3 4/15 + у = 7 11/15
у = 7 11/15 - 3 4/15
у = 4 целых 7/15
Проверка:
3 4/15 + 4 7/15 = 7 11/15
- - - - - - - - - - - - - - - - - -
5 4/13 - х = 4 5/13
х = 5 4/13 - 4 5/13
х = 4 17/13 - 4 5/13
х = 12/13
Проверка:
5 4/13 - 12/13 = 4 5/13
4 17/13 - 12/13 = 4 5/13