/////// Building a- O vvvvvvvvvvvvvv vvvvvvvvvvv'vvv '9'... 9 O... 18am HOW tall is the building?

I broke the initial velocity into its x and y components and used Vx to determine time in s it takes for the rock to hit the ground using eqn R=vxt. I then plugged the time into eqn h=1/2at^2. I am getting the wrong answer. Is my approach to this problem correct? Please explain.

///////Buildinga- O vvvvvvvvvvvvvv vvvvvvvvvvv‘vvv’9’... 9 O... 18am HOW tall is the building? Assume theground is level and that the side of the build-ing is vertical. The acceleration of gravity is9.8 rn/s2 . Answer in units of rn.