Give a detailed example of the recording of purchases under a perpetual inventory system including returns, allowances and discounts. Give a detailed example of the recording sales revenues under a perpetual inventory system including returns, allowances and discounts. Give a detailed example of the recording of purchases under a periodic inventory system including returns, allowances and discounts. Give a detailed example of the recording sales revenues under a periodic inventory system including returns, allowances and discounts. Give an example of how to calculate cost of goods sold under a periodic inventory system. Show all relevant accounts.