Need help on physics homework please.?

Two small beads having positive charges 23q and q are fixed at the opposite ends of a horizontal insulating rod, extending from the origin (the location of the larger charge) to the point x = d. As shown in the figure below, a third small charged bead is free to slide on the rod. At what position is the third bead in equilibrium? http://www.webassign.net/pse/p23-08alt.gif