Section 40. If the state treasurer and the person applying to redeem the mortgage do not agree upon the amount due, the person so applying may bring in the supreme judicial or the superior court, for the county of Suffolk, civil action against the commonwealth for the redemption. The process shall be served on the state treasurer, who shall appear and answer in behalf of the commonwealth; and like proceedings shall be had and like judgment rendered as in case of other mortgagees, except that the state treasurer shall accept any payment due the commonwealth, and upon receipt thereof, or upon performance of such other condition as the court orders, shall discharge the mortgage in like manner as when the debt is paid without suit.