The bus fare in a city is $ 1.25. People who use the bus have the option of purchasing a monthly discount pass for $ 15. With the discount pass, the fare is reduced to $0.50. Using this information, complete parts a through c below.

a. Express the total monthly cost to use the bus without a discount pass, f, as a function of the number of times in a month the bus is used, x.

f(x)=?