Пошаговое объяснение:
1) 1 2/7 + Х = 3 5/7
х= 3 5/7 -1 2/7= 26/7-9/7=17/7=2 3/7
2) 5 9/11 - Х = 2 4/11
-х= 2 4/11-5 9/11= 26/11 - 64/11= - 38/11= - 3 5/11
х= 3 5/11
3) Х + 2 1/4 = 4 3/4
х= 4 3/4- 2 1/4= 19/4- 9/4= 10/4= 2 2/4 = 2 1/2