Answer:
5/2 seconds
Step-by-step explanation:
The ball will return to the ground when the height is 0. So we set the height function to 0 and solve for t.
[tex]-16t^2+40t=0\\16t^2-40t=0\\8t(2t-5)=0\\So\\2t-5=0\\2t=5\\t=\frac{5}{2}[/tex]
t is 5/2 seconds. This is when the ball returns to the ground.
Note: I believe it should be answer choice A and there is a mistake in the answer
