Substitutes shall be paid not less than the minimum salary provided for by section 1142, or in the event they are employed for less than a full school year, the proportionate part of such minimum salary equal to the proportionate part of the school year during which they were employed, arrived at by dividing the number of days during which a substitute was employed by the total number of days the schools of the district were in session during the school year.
24 P.S. § 11-1148