S. 10A : Free trade zone-Set-off losses of STP/SEZ unit against income of non-STP units-Allowed to be set off-Export turnover-Deemed export, reimbursement of expenses, expenses incurred in foreign currency, delayed export proceeds and VAT/GST would form part of export turnover-Corporate office expenses-Allowed on ad hoc percentage of 20 percent and not based on turnover of various undertakings for purpose of deductions under section 10A.[S. 80IB, 80IC]