$5\mathrm{.}4m$ thick clay layer $($drained on one side$)$ has the following properties;

initial void ratio $=0\mathrm{.}6,$OCR$=2,$ current vertical effective stress $=100k\frac{N}{m^2},C_c=0\mathrm{.}2,C_r=0\mathrm{.}05,$

$c_v=1\mathrm{.}53{10}^{-6}\frac{m^2}{sec}.$ This soil has experienced the loading and unloading steps as follows. Please

answer the following questions. $(20$ points$)$

$($a$)$ The final settlement was $0\mathrm{.}3m.$ What is the final effective stress? $($unit: $k\frac{N}{m^2})$

$($b$)$ How long $($in days$)$ will it take for the clay layer to reach $80\%$ consolidation?