ABC Corporation sells industrial equipment. The equipment can be sold independently or combined with maintenance service. In addition, ABC provides maintenance service independently from the sale of the equipment. During 2019 the following transactions take place: 1. On January 15, 175 pieces of equipment are sold. The selling price of the equipment is 5,000 per unit, while the acquisition cost of equipment to ABC is 2,200 per unit. 2. On Mach 1, 240 pieces of equipment combined with 3 years maintenance are sold. The combined price for equipment and the 3-year maintenance service is 6,000 per sale contract. The stand-alone price of the equipment is 5,000 per unit, while the acquisition cost of equipment to ABC is 2,200 per unit. The maintenance service is sold independently for 1,200 per service contract. 3. On April 15, 23 pieces of equipment sold independently on January 15 (transaction 1) are returned from the customers. Although the firm does not adopt a refund policy, in this case fully refunds its customers. 4. On July 1, ABC signed 120 contracts to provide 3 years maintenance services. The stand-alone price of the maintenance contract is 1,200. 5. The net realizable value of ending inventory at December 31, 2019 is 4,200 per unit.

Required: Prepare the journal entries that correspond to the above transactions. In addition, prepare the journal entry for the determination the gross profit of ABC for 2019. Assume that all transactions are in cash. ABCs accounting period starts on January 1 and ends on 31 December of each year. Additional information: -The firm uses a perpetual inventory system. - Assume that the maintenance service is provided linearly during the 3 years period.

Explain the Revenue Recognition Principle and provide a concise presentation of the most recent approaches regarding its content and application. (word limit, 500 words)