$($b$)$ The equilibrium gap when machining $($electro$-$chemically$)$ iron using sodium chloride solution in water as the electrolyte, is found to be $0\mathrm{.}25$ mm with an operating voltage of $18$ volt. Iron dissolves at a valency of $2.$ The specific resistance of the electrolyte is $\backslash (2\mathrm{.}8\backslash$mathrm$\{$ohm$\}-\backslash$mathrm$\{$cm$\}\backslash ).$ Calculate the metal removal rate per unit surface area, if the feed is applied at an angle of $\backslash (15^\{\backslash$circ$\}\backslash )$ to the normal of the work piece. Take the over voltage as $1\mathrm{.}5$ V $.$