Any such city may borrow money or contract indebtedness for strictly municipal purposes over the amount specified in RCW
35.30.040, but not exceeding in amount, together with existing general indebtedness, the amount of indebtedness authorized by chapter
39.36 RCW as now or hereafter amended, to be incurred with the assent of the voters, through the council of the city, whenever three-fifths of the voters assent thereto, at an election to be held for that purpose, at such time, upon such reasonable notice, and in the manner presented by the city council, not inconsistent with the general election laws.