Section 77. Two or more cities or towns in which the establishment of such extended course of instruction has been voted and approved as hereinabove provided may jointly establish and maintain such a course for the accommodation of said municipalities. The management and control of such course of instruction, the location of the schoolhouse where such course will be maintained and the apportionment of the expenses of the maintenance of the course and all incidental expenses shall be determined, on a pro rata pupil basis, by the school committees of the participating towns.