Robert threw a rock off a bridge into the river. The distance from the rock to the river is modeled by the equation h=-16ť – 16t+ 60, where h is the height in feet and t is the time in seconds. Find how long it took the rock to enter the water.​

1.5 seconds

Step-by-step explanation:

h=-16t² – 16t+ 60

When the rock enter the water, the height is 0. ... h=0

0 = -16t² – 16t+ 60 = -4 * (4t² - 4t +15) = -4* (2t - 3) (2t +5)

2t-3=0   or 2t+5 = 0

t = 3/2  or t = -5/2   (time can't be negative)

t = 3/2   or 1.5

1 1/4 hours

step-by-step explanation:

2/4 + 2/4 + 1/4 = 5/4 or 1 1/4

the forst and 3rd

step-by-step explanation: