The amount of financial security shall be equal to one hundred (100) percent of the costs of the required improvements for which financial security is to be posted. The cost of the improvements shall be established from an estimate provided by the Subdivider and approved by the City Engineer. If the Subdivider requires more than one (1) year from the date of posting of the financial security to complete the required improvements, the amount of financial security may be increased by an additional ten (10) percent for each one (1) year period beyond the first anniversary date from posting of financial security or to an amount not exceeding one hundred fifty (150) percent of the cost of completing the required improvements as re-established on or about the expiration of the preceding one (1) year period by using the above procedure.