The surface irregularities of electrodes used in an electrochemical machining (ECM) process are $3 \: μm$ and $6 \: μm$ as shown in the figure. If the work-piece is of pure iron and $12V \: DC$ is applied between the electrodes, the largest feed rate is ___________$mm/min$.
$\begin{array}{|l|l|} \hline \text{Conductivity of the electrolyte} & 0.02 \: ohm^{-1}mm^{-1} \\ \hline \text{Over-potential voltage} & 1.5 \: V \\ \hline \text{Density of iron} & 7860 \: kg/m^3 \\ \hline \text{Atomic weight of iron} & 55.85 \: gm \\ \hline \end{array}$
Assume the iron to be dissolved as $F_e^{+2}$ and the Faraday constant to be $96500$ Coulomb.
