The important thing to note here is that the initial position is to the left of the origin. In fact, that was by our own choosing. Since we chose the initial position to be 50 meters to the left of the origin, the initial position must have a (-) sign. Therefore, the initial position is -50 meters.
The values for initial velocity, acceleration, and time are the same as the ones that we have been using in the previous methods. If you plug those values into the distance formula along with the value that we just got for the initial position, you should be able to get the answer that x = +200 meters.