All developments within the Adult Residential District shall include a set-aside of low- and moderate-income housing units. In recognition of the development difficulties associated with this district and the off-site infrastructure and utility improvements that will be necessary for development within this district, the set-aside shall be as set forth in the Housing Element and Fair Share Plan receiving substantive certification from the Council on Affordable Housing not to exceed fifteen (15%) percent of the total number of dwelling units receiving development approvals. This obligation shall be satisfied by constructing inclusionary units within the development, the funding of units through a regional contribution agreement (RCA), the funding of units to be rehabilitated pursuant to a municipally sponsored rehabilitation program, funding for a municipal housing trust fund, or a combination of the foregoing as may be selected by the Borough. The specific mix of the above alternatives shall be set forth in a written agreement between the Borough and the developer, which agreement shall, among other things, specify the amount and timing of any payments to be made by the developer in lieu of providing inclusionary dwelling units. If the Borough and the developer agree that the set-aside shall be satisfied, in whole or in part, by funding RCA or rehabilitated units or a municipal housing trust fund in lieu of providing inclusionary housing units, there shall be no reduction in the total number of units within the development and all inclusionary housing units being substituted by funded units may be replaced with market housing units.