The possible circular failure surface has a radius equal to 20.2m, and is passing through the toe of cut slope and through the point 4m away on the top ground from the edge of cut. The C.G of the failure mass is at a distance of 9.4m from the center of the failure circle, The properties of soil are C=30kN/m$^{2}$, $\phi =15°$ and $\gamma =20kN/m^{2}$. Find the factor of safety that would be available on failure surface by friction circle method.