Electronic Repair Company repaired a high-definition television for Sarah Merrifield in December 2009. Sarah paid $50 at the time of the repair and agreed to pay Electronic Repair Company $50 each month for five months beginning on January 15, 2010. Electronic Repair Company used $80 of supplies, which were purchased in November 2009, to repair the television.

Required:

1. In what month or months should revenue from this service be recorded by Electronic Repair Company?

2. In what month or months should the expense related to the repair of the television be recorded by Electronic Repair Company?

3. Describe the accounting principles used to answer the above questions.