The manager of PG&E wants a program that calculates a customer's electric bill. He will enter the current and previous meter readings. The program should calculate and display the number of units of electricity used and the total charge for the electricity. The charge for each unit of electricity is $0.11. The program allows the user to display the electric bill for more than one customer without having to run the program again. Use a sentinel value to end the program. Create 3 functions: getInput: Gets the current and previous meter readings from the user. If the user does not enter a sentinel value as the current reading, the getInput function should prompt the user to enter the previous reading. To be valid, the current reading must be greater than or equal to the previous reading. The main function should not call the calcBill or displayBill functions when the readings are not valid. Instead, it should display an error message. calcBill: Calculates both the number of units used and the total charge. displayBill: Displays both the number of units used and the total charge. Input Validation: Do not accept negative numbers for meter readings