Explanation:
The adjusting entry is as follows
On January 31
Unearned revenue A/c Dr $3,500
To Magazine subscription revenue A/c $3,500
(Being the unearned revenue is recorded)
The computation is shown below:
= Sale value of annual subscriptions ÷ total number of months in a year
= $42,000 ÷ 12 months
= $3,500