Sửa đề `3y=7z`
`3x=2y => x/2=y/3 => x/14=y/21`
`3y=7z => y/7=z/3 => y/21=z/9`
`=> x/14=y/21=z/9`
`=(x-y+z)/(14-21+9)`
`=3/2`
`=> x/14=3/2 `
`=> 2x=14.3`
`=> x=21`
`y/21=3/2`
`=> 2y=3.21`
`=> y=31,5`
`z/9=3/2`
`=> 2z=3.9`
`=> z=13,5`
Vậy `x=21; y=31,5; z=13,5`