The cabinet will move with constant velocity only when the net force on it is zero. As the velocity of the cabinet is constant, its acceleration ought to be zero. Therefore, the active force acting on it is also zero. This implies that the magnitude of opposing frictional force is equal to the force exerted on the cabinet, which is 200 N. Therefore, the total friction force is -200 N.
Therefore, the force of friction on the cabinet = 200 N, in a direction opposite to the direction of motion of the cabinet.