A body is thrown upward at speed, u
At 5th and 6th distance travel is equal = $$s$$
Mean in 4sec to 5 sec distance travel = $$s$$
And in 5sec to 6 sec distance travel = $$s$$
It is only possible if body deaccelerated in 4sec to 5 sec and accelerated in 5sec to 6 sec
In projectile motion, this condition is suited, if in 4sec to 5 sec body go upward, and in 5sec to 6 sec body go downward.
So, at 5sec body is at top, and its vertical velocity is zero.
Acceleration of gravity, $$g$$
Initial velocity, $$u$$
Final velocity, $$v$$
Apply kinematic equation at top position.
Hence, body thrown upward at speed $$49\,\,m/s$$