4 2/9x + 3 5/14 = 6 11/21

4 2/9x = 6 11/21 - 3 5/14

4 2/9x = 6 22/42 - 3 15/42

4 2/9x = 3 7/42

4 2/9x = 3 1/6

x = 3 1/6 : 4 2/9

x = 19/6 : 38/9

x = 19/6 * 9/38

x = 3/4

Ответ: 3/4