The City Manager, at least thirty-five (35) days prior to the beginning of each budget year, shall submit to Council a budget estimate and an explanatory budget message. For such purpose, at such date as the City Manager shall determine, the City Manager shall obtain from the director of each department or agency, plans for the work to be undertaken by such organizational unit during the ensuing budget year and estimates of the cost of personnel and material for doing such work, with complete justifications for each project, including all computations, and such other information as the City Manager may request. From the information thus assembled the City Manager shall prepare the budget estimates for Council, revising and adjusting the work programs and departmental estimates as may be required in order to produce a balanced budget.