The mayor, on such date as the board of aldermen may require, but at least thirty-two days before the beginning of any fiscal year, shall submit to the board of aldermen a budget and an explanatory budget message, for that purpose, at such date as he shall determine, the mayor, with the assistance of such city officers and employees as he requests, shall obtain from the head of each office, department, and agency (a) estimates of revenue and expenditures for the next fiscal year, detailed by organization units and character and object of expenditure; (b) such other supporting data as he may request; and (c) an estimate of all capital projects pending or which such office, department, or agency head believes should be undertaken (i) within the budget year and (ii) within the five next succeeding years. In preparing the budget, the mayor shall review the estimates, shall hold hearings thereon with the head or other representative of the office, department, or agency concerned, and may revise the estimates as he deems advisable. (Acts 1951, ch. 539, § 79)