a retaining wall $4$m high, with vertical back supports a backfill with horizonatl ground surface. The soil has unit weight of $18$Kn$/$m$^3$ and angle of internal friction of $35.$ The angle of wall friction may be taken as $20.$ A footing running parallel to the retaining wall and carrying a load intensity of $18$KN$/$m$,$ is to be constructed. Find the distance of the footing from the face of the wall so that there is no increase in lateral pressure on the wall due to the load of footing