\(\mathop \tau \limits^ \to  \,\, = \,\,(\mathop {{r_1}}\limits^ \to  \,\, \times \,\,\mathop {{F_1}}\limits^ \to  )\,\, + \,\,(\mathop {{r_2}}\limits^ \to  \,\, \times \,\,\mathop {{F_2}}\limits^ \to  )\)

\(\, = \,\,((3,\,0\,,\,0)\,\, \times \,\,(0,\,1,\,0))\,\, + \,\,((0,\,3,\,0)\,\, \times \,\,(0,\, - 1,\,0))\)

\( = \,\,(3\hat i\,\, \times \,\,\hat j)\,\, - \,\,(3\hat j\,\, \times \,\hat j)\,\,\)

\(= \,\,3\hat k\,\,Nm\)