The MPG for a 1995 Pontiac Grand Prix varied depending on the engine. There were several engine options available that year. To get an accurate MPG figure, you need to know which engine was in the specific car. You'll find this information on the vehicle's sticker, usually located in the driver's side doorjamb, or in the owner's manual.
Once you know the engine size (e.g., 3.1L, 3.4L, or 3.8L V6), you can then search online (e.g., using Google or a car specifications website) for the EPA estimated fuel economy for that specific engine and model year. Keep in mind that actual MPG will vary based on driving habits and conditions.