A longwall is experiencing a high average dust concentration of about 2.4mg/ m downwind of the shearer. If the intake air consist of 50,000 cfm (23.6 m) of air containing 0.25mg/ m' of dust, how much air must be coursed through the face to reduce the dust concentration downwind of the shearer to 1.8mg /m if the cross sectional area of the longwall face is 77.5 fr? (7.2 m? ), what is the average velocity of the through the face area after the ventilation is increased? Is this an acceptable velocity?