The x-coordinate of the vertex of a parabolla is:

And b and a, correspond to the standard form of a parabolla:

In this case, we have the parabolla:

Then, the a = 1/3 and b = 0
Using the formula:

Then to find the y coordinate of the vertex, we evaluate the function in x = 0:

The coordinate of the vertex is (0, 0)
Now to find two points on the left and two on the right, we just need to evaluate the function of x at the left and in the right of 0:
Let's use -6, -3, 3, 6

Then the vertex is at:
(0, 0)
We have two points at the left:
(-6, 12)
(-3, 3)
And two to the right:
(3, 12)
(6, 12)