I need help solving the following problem and I would also like to see the steps.

Kielty Company purchased machinery that cost $300,000 on January 1, 2012. The entire cost was recorded as an expense. The machinery has a nine-year life and a $12,000 residual value. Kielty uses the straight-line method to account for depreciation expense. The error was discovered on December 10, 2014. Ignore income tax considerations.

48. Kieltys income statement for the year ended December 31, 2014, should show that cumulative effect of this error in the amount of: A. $236,000. B. $224,000. C. $221,333. D. $ -0-.

49. Before the correction was made and before the books were closed on December 31, 2014, retained earnings was understated by: A. $300,000. B. $236,000. C. $224,000. D. $221,333.