A mass lies on a horizontal surface with friction, initially at rest. A constant force of 6.2 Newtons is applied to the object in the +x direction and this force is enough to overcome static friction and the object slides 7 meters in the +x direction. The net work done by all the forces acting on the mass after it slides this displacment is 17.8 Joules. How much work is done the friction force in Joules? Include a negative sign if it's negative.