Answer:
On December 31, related revenue should be recognized
Step-by-step explanation:
According to the accrual basis of accounting, the recording of the transactions is done when expenses are incurred, and services are rendered to the customers in return the revenues are earned.
It matches the revenues and expenses to a particular year based on weekly, monthly or yearly
In the given case, the projected was completed on December 31 but the payment was received on January 21. So, the revenue should be recognized when the project was completed i.e December 31.