Answer is $65\mathrm{.}88$ pls show me working

A $21\mathrm{.}0$ m thick normally consolidated clay layer is located below a $3\mathrm{.}3$ m thick layer of gravel with density of $\backslash (\backslash$rho$=1\mathrm{.}6\backslash$mathrm$\{$~g$\}/\backslash$mathrm$\{$cm$3\}\backslash ).$ A load of $154$ kPa is applied to the surface over a large extent. A dense sandy gravel exists below the clay layer. The ground water table is located at the top of the clay layer, and submerged density of the soil is $\backslash (0\mathrm{.}93\backslash$mathrm$\{$~g$\}/\backslash$mathrm$\{$cm$\}^\{3\}\backslash ).$ Consolidation tests performed on $2\mathrm{.}1$ cm thick doubly drained samples indicate $\backslash (\backslash$mathrm$\{$t$\}\_\{50\}=2\mathrm{.}06\backslash$mathrm$\{$~min$\}\backslash )$ for a load increment close to that of the loaded clay layer. Compute the effective stress increase in the clay layer at a depth of $16\mathrm{.}0$ m below the ground surface $6$ years after application of the load.

Effective stress increase in kPa :