Consider the following events for betterment incorporated: january 1 betterment purchases gasoline for $200 on account. january 7 betterment advertises lawn mowing services for $100 per lawn. january 9 betterment signs up 8 customers who pay a total of $800 cash. january 12 betterment mows the lawns of the 8 customers and all gasoline purchased on january 1 is used. january 13 betterment pays for the gasoline purchased on january 1. under accrual-basis accounting, what is the appropriate day to record the revenues related to lawn services?