$k=C{d}^2$

Equation $1$

where; $k$ is permeability in units of darcys or $c{m}^2,C$ is a scaling coefficient that varies with

aquifer material, and $d$ is the diameter of the pore openings. A sample of fine sand collected

from an aquifer has an average pore size of $125m.$ If we assume that the coefficient $(C)$ is

$6\mathrm{.}4{10}^{-3},$ then what is the permeability $(k)$ of the fine sand in units of $c{m}^2?$