A truck of mass 9312 kg moving at a speed of 68.7 mph has lost its brakes. Fortunately, the driver finds a runaway lane, a gravel-covered incline that uses friction to stop a truck in such a situation; see the figure. In this case, the incline makes an angle of ? = 21.15° with the horizontal, and the gravel has a coefficient of friction of 0.634 with the tires of the truck. How far along the incline (?x) does the truck travel before it stops?