6 5/27 - (х-1 2/9) = 3 20/81

1) 6 5/27 - (X-1 2/9) = 3 20/81

6 5/27 умножаем на 3=6 15/81

1 2/9 умножаем на 9 = 1 18/81

и так

6 15/81 - (x-1 18/81) = 3 20/81

6 15/81 - 3 20/81 = 2 76/81

2 76/81 + 1 18/81 = 3 94/81=4 13/81

проверка

6 15/81 - (4 13/81-1 18/81) = 6 15/81-2 76/81 = 3 20/81