15points, numéro 60svp, niveau 4ème

a)  (5x-3)(2x-7) = 10x²-35x-6x+21 = 10x²-41x+21

b) (6y+7)(3y-10) = 18y²-60y+21y-70 = 18y²-39y-70

c) (-2x+9)(2x-4) = -4x²+8x+18x-36 = -4x²+26x-36

d) (b-100)(10b-0.2) = 10b²-0.2b-1000b+20 = 10b²-1000.2b+20