Calculation of tds u/s 194ia if service tax amt not separately disclosed in invoice.

What will be the calculation of TDS as per sec 194IA of income tax act 1961 if the amount of bill is a single amount without any descripttion. For calculating service tax we do reverse calculations and find out the service tax. But is this calculation applicable to find out service tax in this section. for example if a invoice of 50000 is raised so tds is on 50000 OR tds is on 50000/112.36 100. Please reply asap.