A parachutist drops freely from an aeroplane for 8 sec before the parachute  opens  out. Then he descends with a net retardation of 2 m/s² reaching the ground with a velocity of 6 m/s . The height from which the bails out of the aeroplane is  $\left(\mathrm{g}=10 \mathrm{m}/{\mathrm{s}}^2\right)$