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 1) ( x - 25 ) - 175 = 0

<=> x - 25 = 175

<=> x = 200

2) 485 - ( 6x + 60 ) = 5

<=> 485 - 5 = 6x + 60

<=> 485 - 5 - 60 = 6x

<=> 420 = 6x

<=> x = 70

3) 315 + ( 135 - x) = 450

<=> 135 -x = 450 - 315

<=> 135 - x = 135

<=> x = 0

4) 346 + ( 210 - x ) = 556

<=> 210 - x = 556 - 346

<=> x = 210 + 346 - 556

<=> x = 0

5) ( x - 32 ) - 68 = 0

<=> x - 32 = 68

<=> x = 68 + 32

<=> x = 100

6) 274 - (9x + 18) = 4

<=> 274 - 4 = 9x + 18

<=> 274 - 4 - 18 = 9x

<=> 252 = 9x

<=> x = 28

7) 442 + ( 418 - x ) = 860

<=> 418 - x = 860 - 442

<=> x = 418 + 442 - 860

<=> x = 0

8) 107 + (210 - x ) = 317

<=> 210 - x = 317 - 107

<=> x = 210 + 107 - 317

<=> x = 0 

9) x - 280 : 35 = 5 . 54

<=> x - 8 = 270

<=> x = 278

10) ( x - 120) : 35 = 5

<=> x - 120 = 5 . 35 = 175

<=> x = 175 + 120

<=> x = 295

11) ( x + 100 ) . 4 = 800

<=>x + 100 = 800 : 4 = 200

<=> x = 200 - 100

<=> x = 100

12) x . 5 + 10 . 9  = 990

<=> x . 5 + 90 = 990 

<=> x . 5 = 990 - 90

<=> x . 5 = 900

<=> x = 180