#### Answer

14.5 m

#### Work Step by Step

Calculate the horizontal displacement as the horizontal velocity multiplied by the time:
(12.2 m/s)(t) = 21.0 m.
Solve for the time of 1.72 s.
Find the roof height from equation 2.11b applied to the vertical motion. The acceleration is g, the initial vertical velocity is zero, and the time is 1.72 s.
The roof height is 14.5 m.