$21$

Given the following data for a particular inventory item:

$00$:$12$:$47$

$\backslash$table$[[$Demand:$,500$ units per month$],[$Ordering Cost:,$$30$ per order$],[$Holding Cost:,$$1$ per unit per year$],[$Lead Time:,$1\mathrm{.}5$ months$],[$Price:$,$$$7\mathrm{.}99$ per unit$],[360$ working days in a year$]]$