In addition to the notice requirements of the general election law, whenever a proposition to increase a tax rate under Section 3-14 is submitted to be voted upon by the voters of any community college district the notice of such election shall include an estimate of the approximate amount of taxes expendable under the maximum rate then in force and an estimate of the approximate amount of taxes extendible under the proposed increased rate, such amounts being computed upon, the last known equalized, assessed value, but any error, miscalculation or inaccuracy in computing such amounts shall not invalidate or affect the validity of any rate so increased. The board shall make such estimate and the secretary shall certify such amount to the election authority as part of the certification of the proposition as required by the general election law.