a) 16x-2y-15y+20x = 36x-17y
b) 14x²-21+24-4x² = 10x²+3
c) 5x(x+4)-(x+4)-3x²+9 = 5x²+20x-x-4-3x²+9 = 2x²+19x+5
d) 7(x+2)-x(x+2)-3x(4-x)-(4-x) = 7x+14-x²-2x-12x+3x²-4+x = 2x²-6x+10
e) (2x³-8x³) : x² = -6x³ : x² = -6x
