Modify the Coffee class so that cost takes into account
bulk discounts:
. . . Develop a program that computes the cost of
selling bulkcoffee at a specialty coffee seller from a
receipt that includes the kind of coffee, the unit price,
and the total amount (weight) sold. If the sale is for
less than 5,000 pounds, there is no discount. For sales
of 5,000 pounds to 20,000 pounds, the seller grantsa
discount of 10%. For sales of 20,000 pounds or more,
the discount is 25%. . . .