Andrew Electronics Repairs uses $28,800$ units of a part each year $($an average of $80$ units per working day$).$ It costs $$25$ to place and receive an order. Andrews orders in lot sizes of $320$ units and it costs $$2\mathrm{.}50$ to carry one unit per year in inventory.The economic order quantity is:a$.800$b $759$c $461$d$.400$ e$.$ None