A piano of 2.90 kN is lifted by three workers at a constant speed to the apartment 21.3 m above the street by using a pulley system fastened to the roof of the building. Each and every worker is capable to deliver 173 W of power, and the pulley system is 75.0% efficient (so that 25.0% of the mechanical energy is lost due to the friction in pulley). Avoiding the mass of the pulley, determine the time needed to lift the piano from the street to the apartment.