A soil profile consists of a surface layer $2\mathrm{.}76m$ thick of gravel with saturated unit weight of $19\mathrm{.}9k\frac{N}{m^3},$ and bulk unit weight of $15\mathrm{.}9k\frac{N}{m^3}.$ Followed by a $4\mathrm{.}73m$ of clay layer with saturated unit weight of $18\mathrm{.}7k\frac{N}{m^3},$ overlying a base of impermeable rock. The water table is $0\mathrm{.}8m$ below the ground surface. Compute the effective stress at the bottom of the clay layer in kPa. $(2dp).$ Use unit weight of water of $9\mathrm{.}8k\frac{N}{m^3}$