The commission shall establish and collect rentals, which, with the proceeds of sales, will yield an amount sufficient:
(a) To pay the costs of administration and operation of the authority;
(b) To pay the costs of maintaining, operating and improving its properties;
(c) To pay the interest on its contracts or bonds;
(d) To provide a fund for the principal of its contracts and bonds as they come due.
(Added by Stats. 1963, Ch. 1227.)