(a) The Treasurer may deposit the money held in the Treasury in the institutions and upon terms provided by law.
(b) Notwithstanding other provisions of the Charter, the boards of the Proprietary Departments, and of the Departments of Recreation and Parks and Library may grant to the Treasurer the authority to combine money in funds under their respective control with other City money for the purpose of investment. Earnings from the investment of the money of these departments shall be paid by the Treasurer to the department fund from which the money was derived in proportion to the share of the total investment supplied by that fund. The computation of the proportionate shares shall be by a method proposed by the Treasurer, subject to the approval of each of the above boards.