If the mayor shall disapprove of any expenditure line item contained in the budget transmitted to him by the council, he shall, within 10 days of the time of its passage by the council, return the same to the clerk with his objections in writing, and the clerk shall make report thereof to the next regular meeting of the city council, and if four of the council members shall at the meeting adhere to said expenditure line item by yeas and nays and spread upon the minutes, then said expenditure line item shall become effective.