Answer
11.43 s
Work Step by Step
Here we use Fick's law $m=\frac{DA\Delta Ct}{L}$ to find the time.
$m=\frac{DA\Delta Ct}{L}=>t=\frac{mL}{DA\Delta C}$
Let's plug known values into this equation.
$t=\frac{(8\times10^{-13}kg)(0.015\space m)}{(5\times10^{-10}m^{2}/s)(7\times10^{-4}m^{2})(3\times10^{-3}kg/m^{3})}=11.43\space s$
