Physics kinematics problem?

Question

Two stones are thrown simultaneously, one straight upward from the base of a cliff and one straight downward from the top of a cliff. The height of the cliff is 6 m, and the stones are both thrown at a speed of 9 m/s. The height above the ground at which they cross is...

Answer 1

S=V0t -(1/2)gt^2
S=V0t + (1/2)gt^2 -H

V0t -(1/2)gt^2=V0t + (1/2)gt^2 -H
gt^2 -H=0
t=sqrt(H/g)

S=V0t -(1/2)gt^2
S=V0sqrt(H/g) - (1/2)H
S=9 sqrt(6/9.81) - (1/2) 6
S=4.04 m above the ground