Answer: 7 seconds
Step-by-step explanation:
Obtain the time after the ball is thrown at the height of 120 feet.
Substitute s = 120 in s = -16t^2 + 112t + 120 and solve for t as follows:
[tex]\begin{aligned}&120=-16 t^{2}+112t+120 \\&-16 t^{2}+112 t+120-120=0 \\&-16 t^{2}+112t=0 \\&16 t^{2}-112t=0 \\&16 t(t-7)=0 \\&12 t=0, t-7=0 \\&\Rightarrow t=0, t=7\end{aligned}[/tex]
Note that, time cannot be negative or 0. So, ignore t = 0
Therefore, after 7 seconds the ball will reach at a height of 120 feet.