A vertical wall retaining a soil backfill is shown below. Assign the following quantities to dimensions and soil properties: $H_1=4ft,H_2=6ft,$ above water table $=105l\frac{b}{f}{t}^3,{}_{\text{s}\text{a}\text{t}}=122l\frac{b}{f}{t}^3,{}^{\text{'}}=30($both above and below water table$),c^{\text{'}}=0,$ and $q=0.$ Plot the variation with depth $($z$)$ of the at$-$rest lateral earth pressure behind the wall, and determine the magnitude and location of the at$-$rest lateral earth force per unit length of wall.