Answer:
rent expense 2,100 debit
rent prepaid  2,100 credit
        cash        4,200 credit
rent expense  2,100 debit
     rent prepaid      2,100 credit
cash     16,200 debit
   unearned revenue    16,200 credit
unearned revneue 8,100 debit
  service revenue     8,100 credit
prepaid insurance  3,150 debit
         cash          3,150 credit
insurance expense 1,050 debit
  prepaid insurance    1,050 credit
Explanation:
A) one month is rent expense while the other prepaid.
4,200 / 2 months = 2,100
at october 31th we accrued the month rent expense and decrease the payable
B) this will be unearned revenu
at month end we recognize half as there are two events and one has already occur
16,200 / 2 = 8,100
C) similar to A but this time the contract is for three mont hand all are prepaid when paying.
3,1050 / 3 = 1,050
at the end of the month, we adjust and recognze insurance expense.