Answer: 4.47 seconds.
Step-by-step explanation:
Hi, the rock will reach the river when the height (h) is 0.
So, replacing in the equation given:
h= -16t2+320
Where t is the time
0= -16t2+320
Solving for t
-320 = -16t2
-320/-16 =t2
20 = t2
√20 =t
4.47 = t
Assuming that t is the time in seconds, the rock will reach the river after 4.47 seconds.
Feel free to ask for more if needed or if you did not understand something.
