The fuel economy of a 2007 Ford Mustang varies significantly depending on the engine type (V6 or V8) and whether it's an automatic or manual transmission. There's no single MPG figure. You'll need to specify the engine to get a more accurate answer.
You can find the EPA estimated MPG for the specific 2007 Mustang model on the Ford website's archive or sites like fueleconomy.gov (in the US).
