A flexible wall is shown below. If the wall moves to the left but remains stable, the backfill soil will be in an active state. $($a$)$ Using Rankine earth pressure theory, perform an Effective Stress Analysis $($ESA$)$ to calculate and sketch the distribution of total lateral stress along the retained height of the wall. $($b$)$ Calculate the magnitude and location of the resultant force based on the total stress distribution from part $a.($c$)$ How much must the wall move at a minimum at its top to mobilize the active pressures?