A = ( 71 + x ) - ( -24 - x ) + ( -35 - x )
= 71 + x - ( -24 ) + x + ( -35 ) + x
= 71 - ( -24 ) + ( -35 ) + x . 3
= 60 + 3x
= 3 ( 20 + x )
B = x - 34 - [ ( 15 + x ) - ( 23 - x ) ]
= x - 34 - [ 15 + x - 23 + x ]
= x - 34 - ( 15 - 23 ) - 2x
= x - 34 - ( -8 ) - 2x
= x - 26 - 2x
= ( -x ) - 26
C ) tương tự