#### Answer

a. $16500-50x$,
b. $16500x-50x^2$

#### Work Step by Step

a. We can express the relation between the number of passengers and the ticket price as $N(x)=9000+50(150-x)=16500-50x$, so that $N(150)=9000$ and $N$ increases by 50 for every dollar decrease in price.
b. The revenue can be expressed as $R=Nx=16500x-50x^2$