Answer:
Debit cash $7800
Credit unearned revenue $7800
Explanation:
The amount of $7800 was received in cash on October 1. Therefore, the cash account will be debited with the $7800 received.
The corresponding credit entry of $7800 will be to the unearned revenue account since the revenue has not been earned. Revenue will be earned at the end of each month of the lease. This account will subsequently debited each time the revenue is earned i.e at the end of each lease month.