Whenever the board of directors of any school district shall deem it advisable to validate and ratify the indebtedness mentioned in RCW 28A.535.010, they shall provide therefor by resolution, which shall be entered on the records of such school district, which resolution shall provide for the holding of an election for the purpose of submitting the question of validating and ratifying the indebtedness so incurred to the voters of such school district for approval or disapproval, and if at such election three-fifths of the voters in such school district voting at such election shall vote in favor of the validation and ratification of such indebtedness, then such indebtedness so validated and ratified and every part thereof existing at the time of the adoption of said resolution shall thereby become and is hereby declared to be validated and ratified and a binding obligation upon such school district.