The plan for covering the members of the teachers' retirement system under the old age and survivor insurance provisions of Title II of the federal social security act as amended, required by RCW 41.48.050 as amended by section 5, chapter 4, Laws of the Extraordinary Session of 1955, approved by the board of trustees of the teachers' retirement system on October 8, 1956, and by the governor of the state of Washington on November 19, 1956, is hereby approved.