secondary office meaning in English

二级交换局

Investment rate of return to the secondary office , how to calculate
想投资二手写字楼年回报率该如何计算？
As a result of the decline of the property market , some companies previously moved to secondary office nodes because of lower rent have moved back to the central business district
因为地产?场不景气，某些公司过往曾因地租便宜，搬至次要办公室区域，现在已迁回商业中心地区。