moment

A beam AB has length 6 m and weight 200 N. The beam rests in a horizontal position on two supports at points C and D, where AC =1 m and DB =1 m. Two children, Sophie and Tom, each of weight 500 N, stand on the beam with Sophie standing twice as far from the end of B as Tom. The beam remains horizontal and in equilibrium and the magnitude ov the reaction at D is three times the magnitude of the reaction at C. By modelling the beam as a uniform rod and the two children as particles, find how far is Tom standing from the end B.