InfoPath Dev

Thanks Shilpa Problem is I can't get the code right that goes in this rule. Are you able to help me here?

I am a newby to Infopath - and am creating an advertising budget form. Everything is going well so far - but now I need to total some repeating columns and I am getting stuck. I have a XML datasource with ID/AdvertPub/AdvertBook/AdvertCosts which fill a repeating table as follows : Drop down box selects AdvertPub, which then autofills ...