Пошаговое объяснение:
9 5/28 - 7 1/2 + x = 2 4/21
9 5/28 - 7 14/28 + x = 2 4/21
1 19/28 + x = 2 4/21
x = 2 4/21 - 1 19/28
x = 2 16/84 - 1 57/84
x = 43/84
