Precalculus (6th Edition) Blitzer

a. $40000-500x$ b. $40000x-500x^2$
a. We can express the relation between the number of spectators and the ticket price as $N(x)=30000-500(x-20)=40000-500x$ so that $N(20)=30000$ and $N$ decreases by $500$ for every dollar increase in price. b. The revenue can be expressed as $R=Nx=40000x-500x^2$