taking downward direction as +ve

we know that

s=ut+1/2at^2

u=0
a=g

s=1/2gt^2

or

s=4.9 t^2.........(x)

put the values of t for diff balls
difference b/w thrownig of 6th and 5th ball is 1 sec

 

put in (x) u get 4.9 m

 

difference b/w thrownig of 6th and 4th ball is 2 sec

 

put in (x) u get 19.6 m

 

similarly do other one

nudge if u hav doubt
rate if u like !!