Exchange rate in asset capitalization

1) You have imported a machinery on 10-07-2011

2) Machinery erection date- 15-05-2013(i.e Date of Capitalization)

3) The value of Machine is $25000

4) Advance payment of 25% was made on 19-05-2011

5) Balance 75% of the amount was settled on 16-06-2013

 what Exchange rate we should take wen we book the asset? with reason.