Powell Company had the following errors over the last two years:

2007: Ending inventory was overstated by $30,000 while depreciation expense was overstated by $24,000.

2008: Ending inventory was understated by $5,000 while depreciation expense was understated by $4,000.

By how much should retained earnings be adjusted on January 1, 2009? (Ignore taxes)
a. Increase by $15,000.
b. Decrease by $25,000.
c. Decrease by $6,000.
d. Increase by $25,000.