At the end of each quarter, or at the close of any canning season that does not exceed three consecutive months, the state department shall determine the actual cost of inspection and laboratory control of each separate food product for the preceding quarter or preceding canning season, and shall prorate the cost to each person licensed under this chapter on the basis of cases packed, tons packed, or number of man-hours necessary to be employed, whichever has been determined by the Cannery Inspection Board, with the approval of the state department, to be most

equitable.