After the tentative apportionments of cost have been made, the drainage board shall set a time, date, and place it will meet and hear objections to the apportionments. Notice of the hearing shall be published twice in each county involved by inserting the notice in at least 1 newspaper published in the county, designated by the drainage board. The first publication is to be not less than 20 days before the time of hearing. The notice shall also be sent by registered mail to the clerk or secretary of each public corporation proposed to be assessed, except that a notice to the state shall be sent to the state highway director and a notice to a county shall be sent both to the county clerk and the county road commission. The mailing shall be made not less than 20 days before the time of hearing. The notice shall be signed by the secretary and proof of the publication and mailing of the notice shall be filed with the secretary. The drainage board may provide a form to be substantially followed in the giving of the notice. The notice shall include tentative apportionments to the several public corporations. After the hearing, the drainage board may confirm the apportionments as tentatively made, or, if it considers the apportionments to be inequitable, it shall readjust the apportionments. Before readjusted apportionments are confirmed, the drainage board shall set a time, date, and place for a rehearing and shall give notice of the hearing. The notice shall also set forth the apportionments as readjusted. It shall then issue its order setting forth the several apportionments as confirmed. The order shall be known as the final order of apportionment.