Within 30 days after the receipt of an annexation petition from a petitioning district, the board of the annexing district shall, if it favors the annexation, adopt a resolution setting forth its intention to annex the petitioning district, and shall cause the resolution of intention to annex to be published once a week for at least three weeks in a newspaper of general circulation in the county in which the office of the annexing district is situated. The board shall state in such publication the date when the board proposes to finally act upon the petition for annexation, which date shall be at least 40 days after the first publication of the resolution of intention to annex.