CBSE Class 9 Answered

average velocity =( v_o + v) / 2

distance travelled  is(  x =  v ' t, where v'  = (v_o + v ) /2 

subsituting the value in above equation

you will get x =  (v_o   +  v_o  + at ) t / 2

and finally x =  vo t +  at² / 2 , in this equation replace x with h,  vo with u and as the body is moving under gravity (opposite to gravity repace a with (- g ))  solve the equation and get the answer,

Vo is the initial velocity x is the distance covered , h is the height