A stone is projected from ground and hits a smooth vertical wall after 1 sec. and again falls back on the ground. The time taken by stone to reach the ground after the collision is 3 secs. In collision with the wall, only horizontal component of velocity of stone changes. Find the maximum height (in metres) reached by the same stone if the vertical wall were not to be present .   $(\text{g }=\text{1}0\text{ m}/{\text{s}}^{\text{2}})$