Can anyone break down the process of answering this question? I am missing some steps.

Griffin ( ny had the following inventory information for the year ending December 31: Units Unit Cost Total Beginning Inventory 30 $12 $360 Purchases: March 3 20 10 200 June 15 30 9 270 September 28 55 7 385 Cost of Goods Available for Sale 135 $1,215 On December 31, Griffin Company had an ending inventory of 35 units. They use a periodic inventory system to compute the cost of ending inventory. Required: Using LIFO: (a) Compute the cost of ending inventory (b) Compute the cost of goods sold Cost of ending inventory: $ 1I Cost of goods sold: $0