A petition seeking the withdrawal of land from such district signed by the legal voters in the area proposed for withdrawal equal in number to ten percent of the number of votes cast for Governor at the last general election may be filed with the board of directors. If the board finds that the portion of the district that would remain after such proposed withdrawal would have a minimum taxable valuation of eight million six hundred thousand dollars, it shall submit the question of withdrawal of such area to the legal voters of the district at the next annual hospital district election. If a majority of those voting on the question in the area sought to be withdrawn and a similar majority in the remaining portion of the district vote in favor of such withdrawal, the board of directors shall declare such area withdrawn and certify the altered boundaries of the district to the county board of the county in which the withdrawn area is located and of the county in which the greater portion of the district is located.