Engine Central had the following sales transactions in December:

Dec.	4		Sold $4,200 of merchandise on account to Mos Motors, terms 2/15, net 30. Cost $2,100.
	7		Mo returned $1,200 of merchandise to Engine Central because he changed his mind and wanted to order a different type of engine. Cost $600.
	16		Mo paid the balance owing to Engine Central.

Prepare the journal entries to record the sales transactions on the books of Engine Central using a perpetual inventory system and the earnings approach for revenue recognition