A $20\mathrm{.}0-$m$-$long uniform beam weighing $660$ N rests on walls A and B$,$ as shown in the figure.

Find the maximum weight of a person who can walk to the extreme end D without tipping the beam.

Find the forces that the walls A and B exert on the beam when the person is standing at D$.$

Find the forces that the walls A and B exert on the beam when the person is standing at a point $3\mathrm{.}5$ m to the right of B$.$

Find the forces that the walls A and B exert on the beam when the person is standing $4\mathrm{.}0$ m to the right of A$.$