Untitled

                    let $channel := 
                        for $ch in $sr/sr/channels/channel
                        where $ch/name = "P6"
                        return $ch
                    
                    let $program := 
                        for $p in $sr/sr/programs/program
                        where $p/channel = $channel/@id
                        return $p

                    let $broadcast := 
                        for $b in  $sr/sr/broadcasts/broadcast
                        where $b/program = $program/@id
                        return $b

                    return sum($broadcast/duration)