An electricity company charges its customers a fixed base charge of $6 a month, plus 10 cents per kilowatt-hour (kWh) for the first 500 kWh, 11 cents per kWh for the next 500 kWh, and15 cents for all additional kWh. (a) Express the monthly cost E as a function of the amount x of electricity used. (b) Graph the function E for 0 < x < 2000. (c) Explain how your graph represents your function E.