PLEASE SOLVE THE SECOND PART

Assuming the ultimate primary consolidation settlement $($S$\_($c$))$ for the clay layer in the previous

profile is $1$ ft $.,$ and its coefficient of consolidation is $5$xx$10^(-6)$ft$^(2)//$s$,$ answer the following questions:

a$)$ How long $($in years$)$ would it take for $0\mathrm{.}5$ ft $.$ of settlement to take place? $(5$pts$)$

b$)$ If a sand layer was found below the clay layer instead of the bedrock shown in the figure,

how long $($in years$)$ would it take for the same $0\mathrm{.}5$ ft $.$ of settlement to take place? $(5$pts$)$

c$)$ Why would the settlement rates observed in the field be more rapid than your

estimations? $(5$pts$)$