Answer:
6 seconds
Step-by-step explanation:
First: equalize the equation to zero
f(t) = -5t² + 20t + 60
-5t² + 20t + 60 = 0
Second: find its roots
-5(t² - 4t - 12) = 0
-5 (t - 6)(t + 2) = 0
[tex]t - 6 = 0 \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: t + 2 = 0 \\ t = 6 \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: t = - 2[/tex]
Time can't be negative so the answer is: it takes 6 seconds to hit the ground
