The Commission shall have power to determine that the whole or any part of the expense of any public improvement shall be defrayed by special assessments upon the property especially benefitted and shall so declare by resolution. The resolution shall include the estimated cost of the improvement, what proportion of the cost shall be paid by special assessment and what part, if any, shall be a general obligation of the city, the number of installments in which assessments may be paid, and the districts of land and premises upon which special assessments shall be levied. The resolution shall provide for a separate hearing on necessity.