Before the municipality may institute annexation proceedings, the Council shall provide an opportunity for all interested persons to be heard at two public hearings to be held not more than 40 days nor less than 20 days prior to consideration of the ordinance annexing the property. If within 10 days after the publication of the notice required herein, more than 20 adult residents who reside in the territory proposed to be annexed protest in writing to the Municipal Secretary of the institution of the annexation proceedings, then at least one of the public hearings must be held within the area proposed to be annexed. Each written protest shall contain the name, address, and age of each signatory.