Prepare the necessary journal entries to record the following transactions, assuming Darby Company uses a perpetual inventory system. (a) Darby sells $50,000 of merchandise, terms 1/10, n/30. The merchandise cost $30,000. (b) The customer in (a) returned $5,000 of merchandise to Darby. The merchandise returned cost $3,000. (c) Darby received the balance due within the discount period