The cost to hire a caterer for a party depends on the number of guests attending. If 100 people attend, the cost per person will be 20 dollars. For each person less than $100,$ the cost will increase by 5 dollars. Assume that no more than 100 people will attend. Let $x$ represent the number less than 100 who do not attend. For example, if 95 attend, then $x=5$
(a) Write a function $N(x)$ giving the number of guests.
(b) Write a function $G(x)$ giving the cost per guest.
(c) Write a function $N(x) \cdot G(x)$ for the total $\operatorname{cost}, C(x)$
(d) What is the total cost if 80 people attend?