Prepare journal entries to record each of the following purchases transactions of a merchandising company. Show supporting calculations and assume a perpetual inventory system.

Mar. $5$ Purchased $500$ units of product at a cost of $$5$ per unit. The purchaser was granted a trade discount of $20\%$ and the terms of the sale were $2/10,$ n$/60.$

Mar. $7$ Returned $50$ defective units from the March $5$ purchase and received full credit.

Mar. $15$ Paid the amount due from the March $5$ purchase, less the return on March $7$ and applicable discount.