Answer:
Question requires the journal entries to record a, b and c.
a.
Date Account Title Debit Credit
2018 Cash $490,000,000
Unearned revenue $490,000,000
b.
Date Account Title Debit Credit
2018 Unearned revenue $239,000,000
Service revenue $239,000,000
c.
Date Account Title Debit Credit
2019 Unearned revenue $251,000,000
Service revenue $251,000,000