The registrar of motor vehicles, within fifty days after receipt of report of any motor vehicle accident, or after receipt of additional evidence as may be requested by the registrar, and upon determining the amount of security to be required of any person involved in such accident or to be required of the owner of any motor vehicle involved in such accident, shall give written notice to such person of the amount of security required to be deposited by him. Such notice shall inform the person of his right to a hearing if written request is made within thirty days of the mailing of the notice.