You'll need to specify the engine size (e.g., 4.2L V6, 4.6L V8, 5.4L V8) to get a more accurate estimate. Even then, the actual MPG will depend on driving conditions and maintenance.
To find the EPA estimated MPG, I recommend checking the official EPA website's FuelEconomy.gov or searching online for "2007 Ford F-150 MPG [engine size]" replacing "[engine size]" with the specific engine of your truck.