how do i get the cost per unit for decemeber 15th?

Required information [The following information applies to the questions displayed be Trey Monson starts a merchandising business on December 1 and enters into the following three inventory purchases. Monson uses a perpetual imventory system. Also, on December 15 , Monson sells 15 units for $22 each Determine the costs assigned to ending inventory when costs are assigned based on the weighted average method: Note: Round your per unit costs to 2 decimal ploces