A mathematical conundrum =) Help?

Our school has an athletic track that goes around our rugby field and it (the track) is 390m in length. We have a track event that is 3000m and have a problem figuring out our starting line. Because a standard athletics track is 400m. The oval shaped circuit's sides are both about 100m (or should be) and the curved parts are about the same. So we would like to know where to start on the track to to end on the end one of the sides. Any help?