Answer:
5 seconds
Explanation:
When the rocket is on the ground, then h = 0 , that is
- 6t² + 30t = 0 ← factor out - 6t from each term
- 6t(t - 5) = 0
Equate each factor to zero and solve for t
- 6t = 0 ⇒ t = 0 ← when rocket is launched
t - 5 = 0 ⇒ t = 5 ← time when rocket returns to ground