The corrosion potential of iron immersed in a de-aerated acidic solution of pH = 3 is −0.720 V as measured at 25°C relative to the standard calomel electrode with potential 0.2802 V. A Tafel plot of cathodic current density against overpotential yields a slope of 18 V−1 and the hydrogen ion exchange current density j0 = 0.10 μA cm−2. Calculate the corrosion rate in milligrams of iron per square centimetre per day (mg cm−2 d−1).