Answer:
It is 5 seconds option C
Step-by-step explanation:
When the ball would hit the ground, h would reduce 0.
We can equate the R.H.S to 0.
∴ 0= -16t²+64t+80
0 = t² - 4t - 5 (dividing both sides by -16)
0 = t²+t - 5t -5 (by splitting the middle term)
0 = t ( t+1) -5 (t+1)
0= (t-5) * (t + 1)
when t-5=0 ; when t+1=0
t =5 ; t= -1 time cannot be -ve
∴ t= 5 seconds
Hope this helps you.
