Section 42C. A professor or teacher in the Bradford Durfee College of Technology or the New Bedford Institute of Technology, who is not employed in a position classified under chapter thirty-one, and who has served as such for three consecutive years, shall not be dismissed from such employment except for just cause, and for reasons specifically given him in writing by the trustees of the college or institute in which he is employed. Before any such removal is effected, the professor or teacher, upon his written request made within ten days of receipt by him of the required written notice, shall be given a full hearing before the trustees of the college or institute in which he is employed, of which hearing he shall have at least thirty days’ written notice from the trustees, and he shall be allowed to answer the charges preferred against him either personally or by counsel.