Answer:
a) Minimum acceleration is
.
b) It will take
.
Explanation:
Let's order the information.
Initial velocity:

Final velocity:

Initial position:

Final position:

a) We can use velocity's equation:

⇒

⇒
.
b) For this, equation for average acceleration will be helpful. Taking
and having
as the unknown time it becomes airborne:

⇒

⇒
.