Addison, Inc. uses a perpetual inventory system. Information regarding one inventory item for the month of September follows:

Date Line Item Description Units and Cost

Sep. $1$ Inventory $20$ units at $$20$

$4$ Sold $10$ units

$10$ Purchased $30$ units at $$25$

$17$ Sold $20$ units

$30$ Purchased $10$ units at $$30$

If Addison uses the weighted average cost method, what is the inventory balance at the end of September?