LTCG tax on commercial property

- My brother and I had purchased a office (commercial space) in June 2005 for 16 Lacs,

- which was sold in May 2012 for 34 Lacs.  The money was deposited in our savings account.

- Both of us are equal partners.

- In Dec 2012, we have purchased another office (commercial space) for 85 lacs.

1.  As we have purchased a new office using capital gains from the first office, do we need to pay LTCG tax?

2. If no, under which section we can claim for LTCG exemption?

3. If yes, do we need to pay 20% tax on LTCG after indexation?

Thanks....