` a) 25 - ( 25 - x ) = 12 + ( 42 - 65 )`
`=> 25 - 25 + x = 12 - 23`
`=> x = -11`
` b) 5 + | x+3| = 9`
`=> | x + 3 | = 4`
`TH1 : x + 3 ≥ 0`
`=> x + 3 = 4`
`=> x = 1`
`TH2 : x + 3 ≤ 0`
`x + 3 = -4`
`=> x = -7`
`c) 31 - ( 17 + x ) = 18`
`=> 17 + x = 31 - 18 = 13`
`=> x = 13 - 17`
`=> x = -4`
`d) x - ( - 25 + x ) = 13 - x`
`=> x + 25 - x = 13 - x`
`=> x + x - x = -25 + 13`
`=> x = -12`