(a) To pay the interest accruing on the bonds promptly as it becomes due.
(b) To raise a percentum of the principal of the bonds as will, in equal annual installments, be sufficient to retire all the bonds as they mature.
(2) The funds derived from such tax levies shall be retained by the county treasurer, and kept by the county treasurer in a separate fund to be known as and designated "______ Park and Recreation District bond interest and sinking fund." The fund shall be irrevocably pledged to and used solely for the payment of the interest accruing on and the principal of the bonds when due, so long as any of the bonds or the coupons thereto appertaining remain outstanding and unpaid. The interest earnings of the fund shall be credited thereto and become a part thereof. [Amended by 1969 c.668 §28]