i finished the first two i just need help with the weighted average

Oahu Kiki tracks the number of units purchased and sold throughout each accounting period but applies its inventory costing method at the end of each month, as if it uses a periodic inventory system. Assume Oahu Kiki's records show the following for the month of January. Sales totaled 280 units. Required: 1. Calculate the number and cost of goods available for sale. 2. Calculate the number of units in ending inventory. 3. Calculate the cost of ending inventory and cost of goods sold using the (a) FIFO, (b) LIFO, and (c) weighted average cost methods