write a program called invoice that will prompt the user for items on and invoice and then print the total of the invoice .the program should loop till the person enters -1 the program should have a method named calItem that returns the total for one item and takes as a parameters the quantity and price of the item. the total for an item is the price times the quantity and 0.90 times the price times the quantity for more than 11 items there should be a 10% discount