(a) Arithmetic or calculation errors will be adjusted accordingly in instances that would result in a change of $5,000 or more in a provider's annual reimbursement for either residential habilitation services provided in community residences or day habilitation services.

(b) In order to request a rate correction in accordance with subdivision (a) of this section, the provider must send to Department of Health its request by certified mail, return receipt requested, within 90 days of the provider receiving the rate computation or within 90 days of the first day of the rate period in question, whichever is later.