`71 + 65 . 4 = (x + 140) : x + 260`
`=> 71 + 260 = (x + 140) : x + 260`
`=> 331 = (x + 140) : x + 260`
`=> (x + 140) : x = 331 - 260`
`=> (x + 140) : x = 71`
`=> x : x + 140 : x = 71`
`=> 1 + 140 : x = 71`
`=> 140 : x = 71 - 1`
`=> 140 : x = 70`
`=> x = 140 : 70`
`=> x = 2`
Vậy `x = 2`