Answer :
easy, just make 2 thingummies cancle each other
like this
(2x+3) and (-2x+4)
the sum is 7 because x's cancel
or
(2x-3) and (4x+3),
the sum is 6x because -3 an 3 cancel
like this
(2x+3) and (-2x+4)
the sum is 7 because x's cancel
or
(2x-3) and (4x+3),
the sum is 6x because -3 an 3 cancel