In the event net revenues of the project are insufficient to pay fully the principal and interest on bonds when due, the authority is hereby specifically authorized to pay, and shall pay, all or the remainder of said principal and interest from rental income. The county school board and the trustees of the municipal separate school district are hereby specifically authorized to pay, and shall pay, to the authority, if necessary, such sums as are sufficient to pay all or the remainder of said principal and interest from rental income, and the part of such sum to be paid by the said county school board and the trustees of the municipal separate school district, respectively, to the authority for this purpose shall be determined by the percentage of revenue from the sixteenth section, or lands granted in lieu thereof, to be developed by the authority which each received in the most prior year of receipt.