Section 9. Upon the filing of a petition under section seven, process shall issue and service be made as in suits in equity upon the body politic on behalf of which the assessment was made. Any defence to the petition not relating to the amount of the assessment must be pleaded within thirty days of the return day of the subpoena; but no answer relating solely to the amount of the assessment shall be filed, and there shall be no default for failure to enter an appearance. The trial shall be by the court unless one of the parties within the time prescribed in actions at law files a notice that he desires a trial by jury; and the court may appoint an auditor. Interrogatories may be filed with the same effect as in actions at law. The court, as the request of any party, shall advance the petition so that it may be heard and determined with as little delay as possible. In case petitions have been filed for the assessment of damages and for the abatement of betterments with respect to the same parcel of land and the same public improvement, the petitions shall be tried together. In case of trial by jury, if either party requests it the jury shall view the premises. If the assessment is not reduced the respondent shall recover costs and an execution shall issue therefor as in actions at law; but if the assessment is reduced the petitioner shall recover judgment for costs, and the assessment so determined shall stand as the assessment upon the land, and if it has not been paid shall be collected in the manner provided for an original assessment. If the assessment has been paid judgment shall be entered for the petitioner for the amount of the reduction, with interest at the rate of four per cent per annum from the time of payment.