This question is referring to potential energy, more specifically we can think about gravitational potential energy which we will call GPE. The formula for GPE is:
GPE = mgh
m = mass of substance g = gravitational constant h = height
Therefore, the GPE has a direct linear relationship with height. This suggests that as the height increases, so does the GPE. Now if we look at the image of the train, the train will have the greatest potential energy when it is at the top of the hill (the highest point). At the top of the hill the train will have the greatest height, and therefore, the greatest potential energy.
So the answer is the train has the greatest potential energy at position 1.
