InfoPath Dev

I have a Repeating Table with the following configuration.
Field A: Amount
Field B: Drop down list with values 'Yes' and 'No'

I would like to sum the values in Field A, for those rows whose Field B value is 'Yes', and display it in a new field outside the repeating table.

Can someone help me in achieving this?

Thanks.

Thank you for those who are trying to help me in this.

I have got a solution based on Ted Fitch's response athttp://www.infopathdev.com/forums/topic.asp?TOPIC_ID=2287

Thanks again!!