1. c³/(c²-8c+18)=c³/(c-4)².
2. c³/(c-4)²-c²/(c-4)=(c³-c²*(c-4))/(c-4)=(c³-c³+4c²)/(c-4)²=4c²/(c-4)².
3. c²/(c²-16)-c/(c-4)=c²/((c-4)(c+4))-c/(c-4)=(c²-c*(c+4))/(c²-16)=
=(c²-c²-4)/(c²-16)=-4c/(c²-16).
4. (4c²/(c-4)²):(-4c/(c²-16))=4c²*(c-4)*(c+4)/(-4c*(c-4)²)=-c*(c+4)/(c-4)=
=c*(c+4)/(4-c)=(c²+4c)/(4-c).