After the conclusion of the hearing, and not later than October 2 of each year, and after making any revisions of, deductions from, or increases or additions to, the recommended budget it deems advisable during or after the public hearing, the board shall by resolution adopt the budget as finally determined. Increases or additions shall not be made after the public hearing, unless the items were proposed in writing and filed with the clerk of the board before the close of the public hearing or unless approved by the board by four-fifths vote.