hey hey kirtana and puneet ,

the solution that kirtana has provided is alright no problems with that , the only thing that she has written incorrectly is that " relative velocity in vertical direction " ....because its not the relative velocity in vertical direction , its actually just relative velocity and its direction changes every second . so we write the equation as 

integral of ( relative velocity between two) = relative displacement between two

which is the fundamental equation of kinematics ...............

and the other equation  is quite straightforward.............