State police are investigating a weekend hit-and-run on Interstate 84.  Troopers say a Ford Focus sideswiped a Mustang near westbound Exit 9 shortly after noon on Saturday.  The 28-year old driver told Troopers that he was travelling in the middle lane, and the other driver continued on the highway with damage to the rear driver side corner.  The Carmel man was uninjured, but his car also sustained damage.  The evading vehicle had an Illinois license plate.