If any taxpayer fails, neglects or refuses to make its return as and when required herein the designated official is authorized to determine the amount of tax payable, and by mail to notify such taxpayer of the amount so determined. The amount so fixed shall thereupon be the tax and be immediately due and payable, together with penalty and interest. Delinquent taxes, including any penalty and interest, are subject to an interest charge of 12 percent per year on any unpaid balance from the date the tax became due as provided in LMC 3.52.110 until paid. [Ord. 253 § 1, 2000; Ord. 215 § 1, 1999.]