A retaining wall 4.5 m high with vertical back supports a backfill with horizontal surface. The unit weight of the fill is 18 kN/m3 and the angle of internal friction is 36°. The angle of wall friction may be taken as 18°. A footing running parallel to the retaining wall and carrying a load of 18 kN/m is to be constructed. Search the safe distance of the footing from the face of the wall so that there is no increase in lateral pressure on the wall because of the load of the footing.