Additional Exercise$-$Permeability

A field test in a stratum of sandy soil was made, in which water was pumped from a well which penetrated the full depth of the soil layer. Under equilibrium conditions water was pumped from the well at the rate of $8\mathrm{.}5\frac{m^3}{?}$ day. The observed height of the water level above the horizontal base of the stratum $($which rested on impervious rock$)$ was $4\mathrm{.}5$ m and $5\mathrm{.}5$ m in boreholes made at distances of $15$ m and $30$ m from the well, respectively. Calculate the coefficient of permeability $($in $\frac{m}{?}$ day$).$