The moment about the left end of the plank generated by the vertical force in the right hand support is equal and opposite to the moment about the left end of the plank generated by the weight of the plank. Assuming the plank is uniform such that the center of mass is at the geometric center of the plank, the vertical force due to the weight of the plank acts 2 meters to the right of the left hand support in a downward direction. The vertical force from the right hand support acts on the plank in an upward direction and 4 - 1 = 3 meters to the right of the left hand support:
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