So for this you need to find out what the price would normally be for 20,000 at a price of 19.95 each
20,000 x 19.95 = 399,000
Then find the price of the discount 20,000 at a price of 15.75 each
20,000 x 15.75 = 315,000
Then take to price of the batteries normally 399,000 and minus the price of the discount 315,000
399,000 - 315,000 = 84,000
So the manufacturer would be agreeing to a $84,000 discount.