Set Expected Resolution date to open date 7 days using Script not working

Hi Experts,

I have a requirement to set Expected Resolution Date to open.time 7 days. To meet the requirement I wrote the script as follows

function CalculateDate()
{

       var ticket = new SCFile("rootcause");
       var rc = ticket.doSelect("current.phase=\"Investigation\"");
       var d = 0;
if (rc == RC_SUCCESS)
{
          d= open_time 7;
         ticket.expected_resolution_time=d;
         ticket.doUpdate();
}
} CalculateDate();

While executing this script I am getting error as "Reference Line Error: open.time not defined".

If i try to use some custom Date/string field still I am getting same Error.

Kindly suggest..

Regards,

-DK