I am having difficulty calculating the revenue earned from a 2 year extended warranty after the 90-day manufacture's warranty. Please explain the calculation.

Carnes Electronics sells consumer electronics that carry a 90-day manufacturer's warranty. At the time of purchase, customers are offered the opportunity to also buy a 2 year extended warranty for an additional charge. During the year, Carnes received 448,000 for extended warranties (approximately evenly throughout the year).

How is the earned revenue calculated?