Bonsoir,
A= 6x-15 + 6x²
B= 5xy - (xy -2x) 4 +11y
= 5xy -4xy -8 +11y
= xy +11y -8
C= 12x³ + 56 +4x
D= (6x+3) ( 2x+1)
= 12x² +6x +6x +3
= 12x² +12x +3
E = 4xy + 12x + 14x - 3xy
= xy + 28