physics problem, torque on a table?

[vivofirmus487]

The question is this:

A 20.0 m long uniform beam weighing 560 N rests on walls A and B. Wall A is 3 m from the left edge of the beam and 12 m from wall B. Wall B is 5 m from the right edge of the beam.
(3 m + 12 m+ 5 m=20 m.)

Find the forces that the walls A and B exert on the beam when a person of 560 N is standing 2.0 m to the right of A.

How on earth do you do this? I've been staring at this problem for about an hour. Anyone know how to set this up? Thanks for reading this.