First, we record what we have:
Now, if there are 2 or less question marks, we can solve the problem, so it looks solvable.
The next part would be to pick the correct equation, A first step would be to find the final velocity, this equation is perfect for that:
Now we plug in what we know:
Now, we use what we have now to find the time, this equation is simple and elegant:
And there you go.