There are $1,500$ units of the item in the physical inventory at December $31.$ The periodic inventory system is used.Periodic inventory by three methods

The units of an item available for sale during the year were as follows:

Jan. $1$ Inventory $5,500$ units at $$4$

Feb. $17$ Purchase $6,400$ units at $$6$

July $21$ Purchase $6,000$ units at $$8$

Nov. $23$ Purchase $2,100$ units at $$10$