What happens to the gravitation force between two objects that are 15 m apart, when one of them moves 3 m closer? (Options are seen in the picture provided)

Panel bc in fig. p2.76 is semi-circular, with the 3 meter radius and horizontal straight edge through point b. compute (a) the hydrostatic force of the water on the panel, (b) its center of pressure, and (c) the moment of this force about point b. assume atmospheric pressure on the dry side of the panel