A plane is in level flight at constant speed and each of its two wings has an area of \( 40 \, \text{m}^2 \). If the speed of the air is \( 180 \, \text{km/h} \) over the lower wing surface and \( 252 \, \text{km/h} \) over the upper wing surface, the mass of the plane is ______ \( \text{kg} \). [Take air density to be \( 1 \, \text{kg m}^{-3} \) and \( g = 10 \, \text{m s}^{-2} \)]
