`a,`
`11/12 . x + 3/4 = (-1)/6`
`=> 11/12 x = (-1)/6 - 3/4`
`=> 11/12 x = -11/12`
`=> x = (-11)/12 : 11/12`
`=> x = -1`
Vậy `x = -1`
`b,`
`3 - (1/6 - x) . 2/3 = 2/3`
`=> (1/6 - x) . 2/3 = 3 - 2/3`
`=> (1/6 - x) . 2/3 = 7/3`
`=> 1/6 - x = 7/3 : 2/3`
`=> 1/6 - x = 7/2`
`=> x = 1/6 - 7/2`
`=> x = (-10)/3`
Vậy `x = (-10)/3`