Answer:
FIFO
FIFO means First in First Out. This method values cost of sales at the earliest prices
Cost of Goods Sold = (3,880 units × $8) + (5,430 units × $10)
                 = $85,340
LIFO
LIFO means Last in Fist Out. This method values cost of sales at the latest prices.
Cost of Goods Sold = (8,660 units × $10) + (650 units × $8)
                 = $91,800
Weighted Average Cost
The unit cost is re-calculated with every new purchase of units made. The cost of sale will be valued on the newly calculated average unit cost.
Unit Cost = Total Cost ÷ Total Units
        = (3,880 units × $8) + (8,660 units × $10) / 12,540 units
        = $9.381
Cost of Goods Sold = Units Sold × Unit Cost
                 = 9,310 units × $9.381
                 = $ 87,337.11
