$(10$ points$)$ A clay specimen was tested in the lab consolidation device; its thickness was inch$)$ the top and bottom boundaries were drained. $50\%$ consolidation time on the specimen was obtained in $28\mathrm{.}4$ minutes. Determine

a$)$ the time for $50\%$ consolidation in the field of this soil with a $2\mathrm{.}5m$ thick layer when only the top lay drained

b$)$ the time for $90\%$ consolidation in the field of this soil with a $2\mathrm{.}5m$ thick layer when only the top lay drained

$($Use the data$/$plots given on the next page as needed$)$