The driving moment is computed to be 2800 kN-m and the resisting moment is computed to be 2450 kN-m. It is proposed to reconstruct the slope using several layers of geogrids having allowable tensile force of 20 kN/m. The average centroid of the reinforcement is anticipated to be 8 m away (vertically) from the centre of rotation. Compute the required number of layers of the reinforcement, if the desire factor of safety id 1.5.