(3-5x)^2-(3x-2)(5x+1)=9-30x+25x^2-(15x^2+3x-10x-2)=9-30x+25x^2-15x^2+7x+2=10x^2-23x+11;
6(a-2)(a-3)-4(a-3)^3=(a-3)(6(a-2)-4(a-3)^2)=(a-3)(6a-12-4(a^2-6a+9))=(a-3)(6a-12-4a^2+24a-36)=(a-3)(-4a^2+30a-48)=-4a^3+30a^2-48a+12a^2-90a+154=-4a^3+42a^2-138a+154.