On receiving such notice, the selectboard shall notify all the parties interested of the time when it will examine the premises and hear the parties and their witnesses. They shall apportion the ditch or watercourse among the several parties having regard to the interest of each party in the opening thereof, and shall decide what time each party shall have to open his or her share of the ditch or watercourse, and they may order such ditch or watercourse or a part thereof to be covered, or the selectboard may, if it deems it advantageous and with the written consent of three-fourths of the landowners concerned, place one or more contracts covering all or such portions of said ditch or watercourse as it may deem advisable, and allocate costs in proportion to the benefits received by the interested parties. Such charges shall become a first lien on the property after taxes, and shall be paid to the town treasurer at such time as shall be directed by the selectboard. Funds shall be paid out by the town treasurer on order of the selectboard for costs incurred in drainage. When lands affected lie in more than one town, the selectboard of each town shall appoint one of its own number with authority to act jointly with a similarly appointed representative or representatives from the other town or towns to act in determining the necessity of drainage, allocation of costs, entering into contracts, and other powers as set forth herein.