Part-time employment shall not be used in such manner as to replace full-time personnel or teaching positions. At any time should the number of class hours of part-time personnel in any grade or subject in school equal or exceed 20 hours per week, a full-time teacher shall be employed. The superintendent shall diligently attempt to fill the position as soon as practicable and in accordance with Section 16-22-15. The local superintendent shall keep a record of efforts made to find a qualified teacher, and that record shall be open for public inspection. In the event no qualified applicant is found to fill the vacancy, the superintendent shall immediately re-post the position and notify the State Department of Education and the professional organization, as defined in Section 16-1-30 of the vacancy so that each may publicize the opening. The part-time teacher or teachers may remain in the position for the duration of the school year in which the hiring of a full-time teacher becomes necessary, or until the board approves the hiring of a full-time replacement, whichever comes first. No part-time teacher may be hired to teach in a position from which a full-time teacher resigned or was terminated, unless the teaching unit was subject to reduction-in-force based upon declining enrollment in the grade or subject taught by the full-time teacher.