Draw a triangle with shortest side on the ground (horiz.). The length of this side is 80 feet. Two angles touch the ground: a right angle, and the 70 degree angle.
Then the height of the building is the 2nd shortest side.
The tangent function is the appropriate one to use here: opp h tan 70 deg = -------- = ---------- adj 80 ft h Since tan 70 deg = 2.75, 2.75 = ------- 80 ft
So you want height to be 0 so you plug zero into the height and solve from there. You subtract 192 from both sides to get -192=-16tsquared. Then you would divide by -16 and end up with 12 = t^2. Then you find the square root of 12 and get t = 3.464 seconds.
