a stone is dropped from rest passes the top and bottom of a pole at t1 and t2 respectively then time of passing the mid points

Let the top be at height h1 and bottom h2.
So,
under the effect of gravity, the initial velovity being zero,
h₁= 1/2(gt₁²) ...(i)
and h₂= 1/2(gt₂²) ...(ii)
The mid point is at height of h= (h1+h2)/2 which will be equal to 1/2(gt²) ...(iii)

Find the value of t using i, ii and iii