The Board of Supervisors may enact an ordinance or resolution which has been vetoed by the Mayor pursuant to Section 3.103 if, within 30 days after such veto, not less than two-thirds of the Board of Supervisors shall vote in favor of such measure, except as provided in Section 9.104. If a larger vote is required for the adoption of the measure by provisions of this Charter, such larger vote shall be required to overcome the veto of the Mayor.