#### Answer

It hits the ground after 1.89 s.

#### Work Step by Step

Use equation 2.11 to relate the time of flight to other variables.
When the ball lands, the vertical displacement is 0. The object’s initial vertical velocity is $(18 \frac{m}{s})(sin 31 ^{\circ})$, the final vertical velocity is the opposite of the starting vertical velocity, and the acceleration is $-9.8 \frac{m}{s^{2}}$, negative because it is directed downward.