A - B = ( 2x^4 + 5xy - 2x +5 ) - ( 6x^4 + 3x^3 + 2x - 4 )
= 2x^4 + 5xy - 2x +5 - 6x^4 - 3x^3 - 2x + 4
= ( 2x^4 - 6x^4 ) - ( 2x + 2x ) + ( 5 + 4 ) + 5xy - 3x^3
= -4x^4 - 4x + 9 + 5xy - 3x^3
B - A = ( 6x^4 + 3x^3 + 2x - 4 ) - ( 2x^4 + 5xy - 2x +5 )
= 6x^4 + 3x^3 + 2x - 4 - 2x^4 - 5xy + 2x -5
= ( 6x^4 - 2x^4 ) + ( 2x + 2x ) - ( 4 + 5 ) + 3x^3 - 5xy
= 4x^4 + 4x - 9 + 3x^3 - 5xy
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