During 2021, WMC Corporation discovered that its ending inventories reported on its financial statements were misstated by the following amounts: WMC uses the periodic inventory system and the FIFO cost method. Required: 1-a. Determine the effect of 2019 errors on retained earnings at January 1, 2021, before any adjustments. (Ignore income taxes.) 1-b. Determine the effect of 2020 errors on retained earnings at January 1, 2021, before any adjustments. (Ignore income taxes.) 2. Prepare a journal entry to correct the error in 2021. 3. Will WMC account for the error (a) retrospectively or (b) prospectively? Determine the effect of 2019 errors on retained earnings at January 1,2021 , before any adjustments. (Ignore in (If the answers is no effect then select "No effect" in the dropdown.)