The Commission, after a public hearing and investigation, may establish the prices to be paid producers or associations of producers by distributors in any market, may fix the minimum and maximum wholesale and maximum retail prices to be charged for milk in any market, and may also establish different prices for different grades or classes of milk. The Commission may set different maximum retail prices for the same grade or class of milk on the basis of different methods of distribution. In determining the reasonableness of prices to be paid or charged in any market for any grade, quantity, or class of milk, the Commission shall be guided by all pertinent economic factors relevant to production, processing, and distribution of milk as they affect the public interest in maintaining an adequate supply of milk within the Commonwealth, including compliance with all sanitary regulations in force in such market, necessary operation, processing, storage, and delivery charges, the prices of other foods, and the welfare of the general public. The Commission may adopt a formula incorporating these economic factors that will adjust automatically the prices to be paid producers or associations of producers by distributors in any market, and then provide for the automatic adjustment of resale prices according to the result obtained by the use of this formula. Public hearings shall not be required for price adjustments obtained by use of a formula, but shall be held for adoption or amendment of the formula itself.