At the hearing the board shall also hear and receive any oral or written protests, objections, or evidence which shall be made, presented, or filed. Any person who shall have filed a written protest may withdraw the same at any time prior to the conclusion of the hearing. The board shall have the following powers and duties:
(a) To exclude any territory proposed to be included in a zone when the board finds that such territory will not be benefited by becoming a part of such zone.
(b) To include any additional territory in a proposed zone when the board finds that such territory will be benefited by becoming a part of such zone.