the answer is $20 but i need the explanation why?

The materials manager for a billiard ball maker must periodically place orders for resin, one of the raw materials used in producing billiard balls. She knows that manufacturing uses resin at a rate of 50 kilograms each day, and that it costs $.04 per day to hold a kilogram of retia in inventory. She also knows that the order costs for resin are $100 per order, and that the lead time for delivery is four (4) days. If the order size was 1,000 kilograms of resin, what would be the total daily holding costs