My USA B1/B2 visa expires on 31 August 2012. My question is; up to what date I can enter USA; and if I reach there around 25 August 2012 and needs to over-stay for 15 days or so; is there any way, I can get this extension. Or I would have to leave USA on or before 31 August 2012

Thanks

Kabir Hussain
Lahore, Pakistan