To calculate the work done by the person, we can use the formula for work:
\[ \text{Work} = \text{Force} \times \text{Distance} \times \cos(\theta) \]
In this case, since the person is pushing the box in the same direction as the force applied, \(\theta = 0\) and \(\cos(0) = 1\).
The force applied by the person is 400 newtons, and the distance over which the force is applied is 4 meters.
So, the work done by the person is:
\[ \text{Work} = 400 , \text{N} \times 4 , \text{m} \times 1 = 1600 , \text{joules} \]
The sliding of the box after the person stops pushing does not contribute to the work done by the person, as work is only done when a force is applied.
Therefore, the correct answer is:
1,600 joules