function calculate_cost()
{
   validate_hours()
   var totalhours = 0
      for (i=0;i<document.app.c2903_session.length;i++)
      if (document.app.c2903_session[i].checked)      totalhours += 3
      
      for (i=0;i<document.app.c2079_hours.length;i++)
      if (document.app.c2079_hours[i].checked)        totalhours += parseFloat(document.app.c2079_hours[i].value)
      
      for (i=0;i<document.app.c4789_hours.length;i++)
      if (document.app.c4789_hours[i].checked)        totalhours += parseFloat(document.app.c4789_hours[i].value)
      
   totalhours *= 387
   totalhours = '$' + totalhours + '.00'
   
   document.app.totalcost.value = totalhours
}
function validate_hours()
{
   if (!document.app.selected_course[0].checked)
   {
      disable(document.app.c2903_session)
   }
   else
   {
      enable(document.app.c2903_session)
   }
   if (!document.app.selected_course[1].checked)
   {
      disable(document.app.c2079_hours)
      disable(document.app.c2079_session)
   }
   else
   {
      enable(document.app.c2079_hours)
      enable(document.app.c2079_session)
   }
   if (!document.app.selected_course[2].checked)
   {
      disable(document.app.c4789_hours)
      disable(document.app.c4789_session)
   }
   else
   {
      enable(document.app.c4789_hours)
      enable(document.app.c4789_session)
   }
}
function enable(item)
{
   for (i=0;i<item.length;i++)
   item[i].disabled = false
}
function disable(item)
{
   for (i=0;i<item.length;i++)
   {
      item[i].checked = false
      item[i].disabled = true
   }
}