A 4.0 kg box is sliding on a rough surface back and forth, the distance the box covers in each stroke is 2m. Assume that the box slides left to right in the first stroke, right to left in the second, then left to right at the third, where the box covers a total distance of 6m in the three strokes. Calculate the total work done by friction as this box is sliding back and forth on the rough surface. (The coefficient of kinetic friction between the surface and the box is 0.35).