(4/9 + x) - 1/9 = 7/9

Упростим:

4/9 + x - 1/9 = 7/9

4/9 - 1/9 + x = 7/9

3/9 + x = 7/9

x = 7/9 - 3/9

x = 4/9

Ответ: x = 4/9.