Solution:
(a) Journal entries for December 31, 2020, and December 31, 2021.
          Cash             240,000
          Rent Revenue                 240,000
  (2020 slips - 300 x 800 = 240,000)
          Cash            152,000
     Unearned Rent Revenue              152,000
(2021 slips - 200 x 800 x (1.00 - 0.05) = 152,000)
          Cash             38,400
   Unearned Rent Revenue                 38,400
(2022 slips - 60 x 800 x (1.00 - 0.20) = 38,400)
(b) Rent Revenue for 2020:
Paid in 2012, earned in 2020 Â Â Â Â Â Â Â Â Â Â Â 152,000
Paid in 2013, earned in 2020 Â Â Â Â Â Â Â Â Â Â Â 80,000(100 x 800)
Total                                 232,000