5 ( x - 1 ) - 6 ( x + 1 ) = 7
5x - 5 - 6x - 6 = 7
( 5 - 6)x - 11 = 7
(-1)x = 7 + 11
(-1)x = 18
x = 18 : ( -1 )
x = -18
b ) 4 ( x - 1 ) + 5 ( 1 - x ) = -17
4x - 4 + 5 - 5x = -17
( 4 - 5 )x + 1 = -17
(-1)x = -17 - 1 = -18
x = -18 : (-1 )
x = 18
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