The board shall, on or before the first day in September, fix the rate of taxes, designating the number of cents upon each hundred dollars, using as a basis the value of property transmitted to the board by the county auditor, which rate of taxation shall be sufficient to raise the amount previously fixed by the board. These acts by the board shall constitute a valid assessment of the property and a valid levy of the taxes so fixed, but the rate of taxation shall not exceed the limit imposed by this article.