The diffusion constant for a particular ion crossing a $62\mathrm{.}00$ nm thick artificial membrane is $1\mathrm{.}25$ x $10-16$m$2/$s$.$ The membrane has a surface area of $1\mathrm{.}00$ x$10-15$m$2.$ On one side of the membrane is pure water and on the other side is a solution $0\mathrm{.}400$ x $103$ mol$/$m$3$ of the ions. Initially, what is the number of ions crossing the membrane per second? $($Provide a positive number$)$