Verified answer

(1980:х):30=3

1980:х=30*3

1980:х=90

х=1980:90

х=22

проверка

(1980:22):30=3

90:30=3

3=3

(1980 : х) : 30 = 3

1980 : х = 3 * 30

1980 : х = 90

х = 1980 : 90

х = 22

Ответ. х = 22