A vehicle has a $$20-gal tank and gets$$15 mpg. The number of miles$$N that can be driven depends on the amount of gas$$x in the tank.

1. Write a formula that models this situation.
2. Determine the number of miles the vehicle can travel on (1) a full tank of gas and (2)$$34 of a tank of gas.
3. Determine the domain and range of the function.
4. Determine how many times the driver had to stop for gas if she has driven a total of$$578 mi.