Stones dropped how far apart?

Question

A stone is dropped from the roof of a building. A second stone is dropped 2.50 s later. how far apart are the stones when the second one has reached a speed of 11.0 m/s?

Answer 1

10 = 11 - 0/ t

t = 1.1s (time taken for first stone to reach 11m/s)

since the time of 1.1s is before the 2nd stone is dropped (2.50s), the distance between both stones is the distance travelled by the first stone.

distance travelled by first stone = 1/2 (v+u) t where v is final velocity, u is initial velocity and t is time

=  1/2 (11+0) (1.1)

=6.05m