General Hospital uses disposable diapers at a rate of $200$ per day, with a standard deviation of $20.$ To place and receive a replenishment of diapers from the third$-$party logistics provider typically takes three days. The hospital never wants to run out of diapers, so it holds enough safety stock to ensure $99\mathrm{.}9$ percent availability. Hospital purchasing managers order diapers along with other items every $30$ days. It is time to place an order, and there are $800$ diapers on hand. How many units should be ordered?

Note: Pick the closest answer.