How will the monthly mortgage payment be prorated?

Rosie Malone sold her house to D.M. Band. The contract was signed June 1, 2017, and closing was set for June 25, 2017. Rosie had prepaid her three-year hazard insurance policy in the amount of $1,825.00 on April 1, 2016, and D.M. agreed to assume it at closing. Water and sewer are paid the first of each month for the previous month. They are estimated to total $200 for June. D.M. also agrees to assume Rosie’s mortgage, which will have a balance of $85,385 on date of closing. Monthly payments are $817.83 payable on the first of the month for the previous month. The seller is responsible for day of closing.