om Bergman, owner and operator of the Earplug Superstore, is reviewing the costs associated with the store's best$-$selling hearing aid, the BZ$15.$ The data available to Dr$.$ Bergman concerning this device follow.

Demand $=55$ units$/$week

Order cost $=$ $$4/$order

Holding cost $=$ $$1\mathrm{.}25/$unit$/$year

The Earplug Superstore operates $52$ weeks a year.

If Tom orders at the economic order quantity, how many units does he order at a time?