Local convection heat transfer coefficient for air flowing parallel over a 1-m-long plate with irregular surface topology is experimentally determined to be h_x = 0.5 + 12x – 0.7x³, where h_x is in W/m² .K. If the plate surface is coated with water, determine the corresponding average mass convection coefficient over the entire plate. Assume properties can be evaluated at 298 K and 1 atm.