(2) It shall be the duty of such persons as may be prescribed to pay each year into the Supplementary Fund in such manner and on or before such date as may be prescribed such sums as may be determined by the Assembly of the Supplementary Fund and certified by the Director of the Supplementary Fund, any such sum to be determined in accordance with the returns submitted to the Minister under section 19(1) or, where the person concerned fails or neglects to submit the appropriate return on or before the prescribed date, to pay the Supplementary Fund such sum as may be calculated on an estimate of that person's returns for that year.