Aeroplane = rocket?

Classical Mechanics Level pending

An aeroplane is rising vertically with acceleration $f$ . two stones are dropped from it at an interval of time $t$ . what is the distance between the two stones at time $t'$ after the second stone is dropped?

((g-f)(t+2t'))/2 (t(g-f)(t+2t'))/2 (t(g+f)(t+2t'))/2 t(g+f)(t+2t')