A stage lift raises scenery vertically at a steady speed. In the first stage, the lift exerts an upward force of 1.2 kN1.2\ \mathrm{kN}1.2 kN while raising the scenery through 1.5 m. At an intermediate level, more scenery is added. The lift then exerts an upward force of 1.6 kN1.6\ \mathrm{kN}1.6 kN as it continues to the upper level. The total work done during both stages is 6.6 kJ.
Calculate the vertical height between the intermediate level and the upper level.