[tex]a).(18a-13a)+(16a-24a)=5a+(-8a)=-3a \\ b).2(3a-4b)-3(a-2b)+4(-2a+3b)= \\ =6a-8b-3a+6b-8a+12b=-5a+10b \\ c).(x+3)(x-2)=x^2-2x+3x-6=x^2+x-6 \\ d).(24a^3b):(-6ab)=-4a^2 \\ e).(x-y)(x^2+xy+y^2)-x^3+y^3= \\ =x^3+x^2y+xy^2-x^2y-xy^2-y^3-x^3+y^3=0[/tex]