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.)