`x - 2/3 = 7/12`
`=> x = 7/12 + 2/3`
`=> x = 5/4`
Vậy `x = 5/4`
$\\$
`1/2 . x + 3/5 . (x - 2) = 3`
`=> 1/2 . x + 3/5 . x - 3/5 . 2 = 3`
`=> 1/2 . x + 3/5 . x - 6/5 = 3`
`=> (1/2 + 3/5) . x = 3 + 6/5`
`=> 11/10 . x = 21/5`
`=> x = 21/5 : 11/10`
`=> x = 42/11`
Vậy `x = 42/11`