In May 2006, the Apple Edison Company suplied electricity to residences for a monthly customer charge of $7.58 plus 8.275 cents per kilowatt-hour (kWhr) for the first 400kWhr supplied in the month and 6.208 cents per kWhr for all usage over 400 kWhr for all usage over 400kWhr in the month.

(a) what is the charge for using 300 kWhr in a month?

(b) what is the charge for using 700 kWhr in a month?

(c) If C is the monthly charge for x kWhr. Develop a model relating the monthly charge and kilowatt-hours used. That is, express C as a function of x.