Thank you for your reply, I checked it and tried to fix.
It's working now but I couldn't take offset of the Div because all of the are in the same level, you can find below the code working:
$("#lkWhyUs").click(function()
{ TweenLite.to(window, 10, {scrollTo:3500}); });
but my problem now is the big screens because It will not scrolling to the targert div exactly.
you can check it online: http://www.phantom-uae.com