physics
posted by projectile motion .
A boy sitting on the edge of a vertical cliff fires a rock with a slingshot at a velocity of 16.45758956 m/s and an angle of 59.78 degrees above the horizontal.
The rock lands in a lake at the base of the cliff, a horizontal distance of 89.67 meters beyond the base of the cliff. How high is the cliff in meters?
Please explain steps and how to get there. please Thank you!!!

break the initial velocity into vertical and horizontal components with the sine and cosine.
horizontal distance=vihorz*time
solve for time in air.
in the vertical:
hfinalhinitial= vivert*time4.9t^2
solve for hfinalhinitial. 
i got an answer of y=420.2599461m
is this right??