A mass of 7 kg is compressed into a spring on a horizontal surface. It is compressed into the spring 0.79 meters and held still. The force required is 668 Newtons. It is then released from rest and the mass travels over a originally frictionless, horizontal surface, but at the end of the surface there is some friction with a coefficient of kinetic friction of 0.72. It then travels up a frictionless incline with an inclination angle of 17 degrees. It travels a distance of 4 meters up the incline before it stops. What was the length, in meters, of the portion of the horizontal surface that had friction?