Notwithstanding any other provision of law, when any business establishment is annexed into the corporate limits of a municipality which has a business license tax, the tax for the business concerned for the year in which the annexation became effective shall be prorated so that the amount payable shall be one-twelfth of the annual tax multiplied by the number of full months of the tax year the business was located within the corporate limits. The provisions of this section shall apply to the year 1976 and each year thereafter.