Answer:
1.5713484 seconds.
Explanation:
We can assume the full function as:

Since we want to find time when the phone hits the ground, y should be 0.

Now, we can solve for t:
1) Move 400 to the left side:

2) Divide both side by -162:

3) Find the square root of both sides:

4) This means that:
t = 1.5713484 seconds