Any city, by vote of the qualified electors thereof voting thereon, may become indebted not exceeding in the aggregate an additional ten percent of the value of the taxable tangible property shown as provided in section 26(b), for the purpose of acquiring rights-of-way, constructing, extending and improving the streets and avenues and acquiring rights-of-way, constructing, extending and improving sanitary or storm sewer systems. The governing body of the city may provide that any portion or all of the cost of any such improvement be levied and assessed by the governing body on property benefited by such improvement, and the city shall collect any special assessments so levied and shall use the same to reimburse the city for the amount paid or to be paid by it on the bonds of the city issued for such improvement. For elections referred to in this section the vote required shall be four-sevenths at the general municipal election day, primary or general elections and two-thirds at all other elections.