(a) The comptroller shall withhold from the amount of sales and use tax revenue refunded to a unit of election that has withdrawn from an authority the full amount of the difference between the cost of providing services to persons with disabilities in the unit of election and the fares charged during the period in which the sales and use tax was collected and remit this amount to the authority providing the services.
(b) The authority and the unit of election that has withdrawn shall determine the amount of the cost of providing services to persons with disabilities. If the authority and the unit of election cannot agree on the amount, the comptroller shall determine the amount.