Answer:
t = 5 seconds
Explanation:
We must solve the equation of movement of the ball as a function of time in seconds.
We must find how many seconds it takes until the ball touches the ground. When the ball touches the ground, the height b (t) = 0
Then we equate the equation to zero and solve for t.

Use the quadratic formula.
Where


We take the positive solution
t = 5 seconds