i use the equation range= [(V initial)^2 x (sin 2A)]/[g].
where v inital is 30 m/s and i assume A=45 degrees, and g=9.8 m/s^2
but i got the answer wrong.
You can use the formula
y = yo + v*t - 0.5*g*t^2.
Here v = vo*sinθ
And t = x/vo*cosθ
y is the final position of the rock and yo is the initial position of the rock.