ABC's financial statements for 2020 contained the following error: On December 31, 2020, a fully depreciated piece of equipment (historical cost $4,870.4) was sold for $7,993.8, however, the sale was not recorded. No entries were made to correct this error and temporary 2020 accounts have already been closed. Ignoring any tax effect, the total effect of this error on the balance of retained earnings as of December 31, 2020 is a. overstated by $7993.8. b. overstated by $3123. c. understated by $7993.8. d. understated by $3123.