Answer
a. $12400-60x$,
b. $12400x-60x^2$
Work Step by Step
a. We can express the relation between the number of passengers and the ticket price as $N(x)=7000+60(90-x)=12400-60x$, so that $N(90)=7000$ and $N$ increases by 60 for every dollar decrease in price.
b. The revenue can be expressed as $R=Nx=12400x-60x^2$
