Cullumber Ltd$.\text{'}$s December $31$ year$-$end financial statements contained the following errors:

An insurance premium of $$3570$ was prepaid in $2022$ covering the calendar years $2022,2023,$ and $2024.$ This had been debited to

insurance expense. In addition, on December $31,2023,$ fully depreciated machinery was sold for $$1800$ cash, but the sale was NOT

recorded until $2024.$ There were no other errors during $2023$ or $2024$ and no corrections have been made for any of the errors.

Ignore income tax considerations.

What is the total effect of the errors on the balance of Cullumber's retained earnings at December $31,2023?$

Retained earnings understated by $$630$

Retained earnings understated by $$230$

Retained earnings understated by $$2160$

Retained earnings overstated by $$960$