A group of engineering students constructs a slingshot to launch water balloons. The angle of launch is 30° and the initial velocity of the balloon is 14 m/s. The students launch a balloon from the roof of a building and the balloon lands 42 m away from the building. How tall is the building?

use the formula

y=xtanθ-(g*X^2)/(2*v^2*Cos^2θ)

since it is on he roof,take y=-y=-H=height of the building

where x=42m
θ=30
V=14m/s

note: θ is not included in the exponent 2..just plug-in the value..

God Bless !!!