The amount of the reassessment upon any parcel of land shall be computed by the auditor in the following manner:
(a)
Subtract from the total amount of unpaid assessments including interest and penalties thereon, if any, on all lands to be reassessed, the amount of the total proposed reassessment.
(b)
Prorate the amount of the remainder so ascertained by subtraction, among the respective parcels to be reassessed in accordance with the amounts assessed against each of the parcels in the original assessment.
(c)
Subtract the amount so prorated upon any parcel from the total amount of the unpaid assessment, with interest and penalties thereon, if any, on that parcel and the remainder shall constitute the proposed reassessment on such parcel.