I really need some help with lifo accounting :/ Any help would be very much appreciated. Thanks!

Trey Monson starts a merchandising business on December 1 and enters into three inventory purchase:

Purchases on December 7	10 units @ $ 6.00 cost
Purchases on December 14	20 units @ $12.00 cost
Purchases on December 21	15 units @ $14.00 cost

Monson sells 15 units for $20 each on December 15. Monson uses a perpetual inventory system. Determine the costs assigned to the December 31 ending inventory when costs are assigned based on LIFO.

This is what I have but I'm pretty sure it's incorrect:

I'm really confused.

Perpetual LIFO:	Cost of Goods Available for Sale			Cost of Goods Sold - December 15			Inventory Balance
	# of units	Cost per unit	Cost of Goods Available for Sale	# of units sold	Cost per unit	Cost of Goods Sold	# of units in ending inventory	Cost per unit	Ending Inventory
Purchases:
December 7	10	$6.00	$60	10	$6.00	$60	10	$6.00	$60
December 14	20	12.00	240	5	12.00	$60	5	12.00	60
December 21	15	14.00	210	0
Total	45		$510	15		$120	15		$120