#### Answer

a. $f(x)=2.5x$
b. $g(x)=21+x$
c. $14$ times, $35$ dollars.

#### Work Step by Step

a. Without a discount pass, the monthly cost is $f(x)=2.5x$ where $x$ is the number of times using the bridge.
b. With a discount pass, the monthly cost is $g(x)=21+x$
c. Let the above cost to be equal, we have $2.5x=21+x$ which gives $1.5x=21$ and $x=14$ times. The total cost would be $f(14)=2.5(14)=35$ dollars.