Problem $2)(2$ points$)$ An $8\mathrm{.}5$ m high retaining wall with a vertical back face retains a homogenous clay with a cohesion value of $22$ kPa and zero internal friction angle. The unit weight of the clay is $19\mathrm{.}6k\frac{N}{m^3}.$ a$)$ What is the total lateral earth force on the wall for Rankine active case, $P_a$ after the tension crack happened $($assume that the GW table is very deep$)(1$ point$)?$ b$)$ Determine the location of the resultant $P_a(1$ point$)$