In an arc welding operation, carried out with a power source maintained at 40 volts and 400 amperes, the consumable electrode melts and just fills the gap between the metal plates to be butt-welded. The heat transfer efficiency for the process is 0.8, melting efficiency is 0.3 and the heat required to melt the electrode is 20 J/mm\(^3\). If the travel speed of the electrode is 4 mm/s, the cross-sectional area, in mm\(^2\), of the weld joint is _______