The figure below shows the given force system
The force system above can be replaced by the following three force system shown below where the two pair into a couple which is the couple 480 N·m. The effect of these forces would be the same as the original system.
The two opposing forces above will get canceled, thus, leaving a single force with the same effect as the three forces above which in turn has the same effect to the original system.
Thus, the equivalent single force is 240 N parallel to the given one and at a distance d = 2 m from O. The intercepts of this single force are A(-4, 0) and B(0, 2.31). answer