$5200 is the amount of service revenue should be recorded as an adjusting entry on December 31, 2018
Solution:
Athens Delivery Service is hired on October 31, 2018 to perform services:
=> 6 month contract at $2,600 a month
Then , Nov 1 - Dec 31 = 2 months
i.e 2,600 * 2 = $5200
$5200 is the amount of service revenue should be recorded as an adjusting entry on December 31, 2018