Individual teachers choose from these activities based on their knowledge, skills and interests. (b) TEBA and the Association may agree, by mutual agreement, to act with an arbitration body composed of a single arbitrator and not an arbitration body of three members. In this case, TEBA and the association appoint within fifteen (15) days of operation after the agreement to sue with a single arbitrator, a person who serves as an individual arbitrator. In the event of inability to agree on the person to act as sole arbitrator, either party may request in writing that the Director of Mediation Services has not provided for the necessary appointment. . . .