Problem #$3$

The backfill behind a retaining wall above the water table consists of a sand of unit weight $17k\frac{N}{m^3},$ having shear strength parameters $c=0$ and ${}^{\text{'}}=37.$ The height of the wall is $6$ m and the surface of the backfill is horizontal. Determine the total active thrust per unit length of the wall according to the Rankine theory. If the wall is prevented from yielding, what is the thrust on the wall?

May I know how to solve this question using Rankine theory?