Explanation:
The journal entry at the time of receiving is
Cash A/c Dr $600
To Unearned revenue A/c $600
(Being the cash is received in advance)
Now the adjusting entry is
Unearned revenue A/c Dr $480
To Service revenue A/c $480
(Being the revenue is recorded)
The computation is shown below:
= Number of voice lessons × per lesson
= 8 × $60
= $480