1)2/(3x^2y^2)-5/(5x^3y^2)=(10x-15)/(15x^3y^2)=(5(2x-3))/(15x^3y^2)=(2x-3)/(3x^3y^2)
2)1/(y-3)-6/(y^2-9)=(y+3-6)/(y-3)(y+3)=(y-3)/(y-3)(y+3)=1/(y+3)
3)5/(4a+8)-1/(3a+6)=5/(4(a+2))-1/(3(a+2))=(15-4)/(12(a+2)=11/12(a-2)
4)1/(ab-b^2)-1/(a^2-ab)=1/(b(a-b))-1/(a(a-b))=(a-b)/(ab(a-b))=1/ab
5)6b/(3-b)-2b=(6b-6b+2b^2)/(3-b)=2b^2/(3-b)