The duly certified agency shall prepare and distribute in advance of such referendum all necessary ballots for the purpose thereof, and shall under rules and regulations drawn up and promulgated by said agency, arrange for the necessary poll holders or officials for conducting the said referendum; and following said referendum and within 10 days thereafter the duly certified agency shall canvass and publicly declare the result of such referendum; except that in the event a mail ballot is used, a mail ballot shall be posted by registered mail on a prearranged date at least 30 days following announcement of same to each duly licensed voter by the agency, and a return, self-addressed envelope of suitable size and construction for containing the completed ballot with ample postage affixed shall be enclosed along with complete instructions on the voting procedure, these instructions stating that the ballot should be marked by the voter to indicate and show his preference, then inserted into the return envelope, sealed, and posted or returned within 10 days of the date of the original or first posting, and on a predesignated date and hour at least 15 days after the original mailing and at an open and public meeting, the return envelopes described above shall be opened, the ballots counted, tabulated, and the results publicly declared by the agency or its authorized representatives. (1967, c. 890, s. 11.)