One end of a horizontal string of linear density 4.36�10-4kg/m is attached to a small-amplitude mechanical 56.?

One end of a horizontal string of linear density 4.36�10-4kg/m is attached to a small-amplitude mechanical 56.8Hz vibrator. The string passes over a pulley, a distance L = 1.68m away, and weights are hung from this end. What mass must be hung from this end of the string to produce one loop of a standing wave? Assume the string at the vibrator is a node, which is nearly true.