In case of vacancy in the office of mayor, or in case of the absence of the mayor from the city, or by reason of his/her inability through sickness or other cause to perform the duties of the mayor's office, the council member-at-large, or if he/she is also absent or incapacitated from acting, then such member of said council as the council may by vote designate, shall, during such absence or disability, exercise the powers and perform the duties of the mayor, and while so acting shall be titled "acting mayor", and his/her acts in that capacity shall have the same force and validity as if performed by the mayor.