You have two intervals of constant acceleration: the acceleration part, and the deceleration part.
The questions are asking you about both parts taken together. So,
* Calculate the time over which the first part happens.
* Calculate the time and distance over which the second part happens.
* Add the times and distances for the two parts, and you're done.
Can you take it from here?
Some more hints:
$$x = x_0 + v_0t + at^2/2$$ $$v = v_0 + at$$
To calculate the time for the acceleration part, start with what you know. You know $a$, and you know $x$. (Both $x_0$ and $v_0$ are zero.) The first equation then becomes $t = \sqrt{2x/a}$.