Б-а=в
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9991 4 значное число и кончается на 1
108/(48-3*х)=6 ОДЗ 48-3*х≠0 3*х≠48 х≠16
108=6*(48-3*х)
108=288-18*х
18*х=288-108
18*х=180
х=180/18
х=10
Проверка:
108/(48-3*10)=108/(48-30)=108/18=6
57/5:19/5=285/95=3
51/4:17/2=102/68=1,5
74/3:37/9=666/111=6