GST under Construction Bussinee

Govind (article assitant) (55 Points)

12 October 2017  
If particular flat having Rs.80 Lakh in which I have received Rs.50 Lakh before 30th June 2017 for that we have paid Service Tax and VAT and remaining Rs.30 Lakh I have received after 1st July 2017 then What about taxability on Rs.30 Lakh.
1.I need to calculate GST on just 30 Lakh OR
2.I have to calculate GST on 80 Lakh and then from that GST I have to deduct Service Tax and VAT which I have already paid for 50 Lakh.
PLEASE HELP ME TO EVALUATE AFORESAID LIABILITY.