(6000 - u) - 1980 = 3800

6000 - u = 3800 + 1980

6000 - u = 5780

u = 6000 - 5780

u = 220

Проверка: (6000 - 220) - 1980 = 3800

                   5780 - 1980 = 3800

                   3800 = 3800

Ответ: u = 220.

Verified answer