The board and its officers and employees shall discharge their duties with respect to this system solely in the interest of the participants and beneficiaries:

1. (a) For the exclusive purpose of both of the following:

   1. (1) Providing benefits to members, retired members, and their survivors and beneficiaries.
   2. (2) Defraying reasonable expenses of administering this system.
2. (b) Minimizing the employers’ costs of providing benefits under this part.
3. (c) By investing with the care, skill, prudence, and diligence under the circumstances then prevailing that a prudent person acting in a like capacity and familiar with those matters would use in the conduct of an enterprise of a like character and with like aims.