InfoPath Dev

Can anyone tell me how to sum total cost by Date in a repeating table? i.e. Repeating Table: 8/9/2013 $6.00 8/9/2013 $5.00 8/10/2013 $10.00 Summary: 8/9/2013 $11.00 8/10/2013 $10.00

 I'm attaching a simple sample of this. Save the linked form locally, right click and select design to open in design view - from there you can preview it.

I appreciate your help! Thank you.