`i) ( x - 12 ) - 15 = 20 - ( 17 + x )`
`=> x - 12 - 15 = 20 - 17 - x`
`=> x + x = 12 + 15 + 20 - 17`
`=> 2x = 30`
`=> x = 15`
` k) -12 - | 13 - x | = -21`
`=> | 13 - x | = 9`
`TH1 : 13 - x ≥ 0`
`=> 13 - x = 9`
`=> x = 4`
`TH2 : 13 - x ≤ 0`
`13 - x = -9`
`=> 22`
` 1) 8 ≤ | x - 6 | < 9`
`=> | x - 6 | = 8`
`TH1 : x - 6 ≥ 0`
`=> x - 6 = 8`
`=> x = 14`
`TH2 : x - 6 ≤ 0`
`=> x - 6 = -14`
`=> x = -8`
` m) 720 - [41 - ( 2x - 5)] = 2^3 . 5`
`=> 720 - ( 41 - 2x + 5 ) = 40`
`=> 41 - 2x + 5 = 680`
`=> 46 - 2x = 680`
`=> 2x = 46 - 680`
`=> 2x = -634`
`=> x = -317`