With what speed should a body be thrown upwards so that the distances traversed in the 5th second and 6th second are equal ?

For an object thrown upwards to traverse same distance on 5th and 6th second, the object must change its direction of motion exactly between those two time intervals, i.e., the object reaches the highest point at 5 s. 
So, $\frac{\mathrm{u}}{\mathrm{g}}=5$
u = 5g = 5 x 9.8 = 49m/s