St applicable on what amount

I have to submit a quotation for a big cooling tower system on LSTK basis. The tender documents term it as 'indivisible contract' but price is to be quoted separately for Materials (Supplies) and Services (erection cost). My question: Is ST lapplicable on total lump sum cost of work or just on the cost of services (i.e., erection price).

Please advise urgently. Thanks in advance.