For a field pumping test a well was sunk through a horizontal stratum of sand $14\mathrm{.}5$ thick and underlain by clay stratum Two observation wells were sunk at horizontal distances of $16m$ and $34m$ rspectively from the pumping well. The initial position of the water table was $2\mathrm{.}2m$ below ground level. At a steady$-$state pumping rate of $1850$ litres$/$min$,$ the drandosms in the observation wells were found to be $2\mathrm{.}45m$ and $1\mathrm{.}20m$ respectively. Calculate the coefficient of permeability of the sand.