The amount of money required each year from each city and town of the metropolitan park district to meet the interest, sinking fund requirements, and expenses for each year, and the deficiency, if any, shall be estimated by the general treasurer in accordance with the proportion as determined in § 32-2-8, and shall be included in, and made a part of, the sum charged in the city or town and shall be annually assessed upon it. The general treasurer shall in each year give notice to each city and town of the amount of the assessment, and each of the cities and towns shall pay its respective assessments, into the state treasury, one-half (½) thereof to be paid on or before April 15 and one-half (½) thereof to be paid on or before October 15, in each year.