46 + 4/5 = 46.8

12.6 - 4x = 30

-4x = 17.4

x = -4.35

Проверка:

46 + 4/5 = 46.8

12.6 - 4(-4.35) = 30

12.6 + 17.4 = 30

30 = 30

Ответ: x = -4.35