a) 8x+x=9.12
9x =108
x =108:9
x =12
Vậy x=12
b) 5.3 -5x =4.25
15-5x =100
5x =15-100
5x =-85
x =-85:5
x = -17
Vậy x= -17
=>9x=108
=>x=12
15 - 5x = 100
=>5x = -85
=>-17
\(8x+x=9\times12\)
\(9x=108\)
\(x=108:9\)
\(x=12\)
Vậy \(x=12\)
\(5\times3-5x=4\times25\)
\(15-5x=100\)
\(5x=15-100\)
\(5x=-85\)
\(x=\left(-85\right):5\)
\(x=-17\)
Vậy \(x=-17\)