`(x:12)xx9+8=80`
`(x:12)xx9=80-8`
`(x:12)xx9=72`
`x:12=72:9`
`x:12=8`
`x=8xx12`
`x=96`
\(\left(x:12\right)\times9+8=80\)
\(\Rightarrow\left(x:12\right)\times9=80-8\)
\(\Rightarrow\left(x:12\right)\times9=72\)
\(\Rightarrow x:12=72:9\)
\(\Rightarrow x:12=8\)
\(\Rightarrow x=12\times8\)
\(\Rightarrow x=96\)
Vậy x=96