30 * (11х/6 + 16/5) = 231
11х/6 + 16/5 = 231/30
11х/6 + 16/5 = 77/10
11х/6 = 77/10 - 16/5
11х/6 = 77/10 - 32/10
11х/6 = 45/10
х = 45/10 : 11/6
х = 45/10 * 6/11
х = 27/11
Проверка: 30 * (11/6 * 27/11 + 16/5) = 30 * (9/2 + 16/5) = 30 * ( 45/10 + 32/10) = 30 * 77/10 = 231 - верно
Ответ: 27/11