If the pressure angle of the worm is , what is the axial pitch of the worm?

Question

Speed reduction in a gear box is achieved using a worm and worm wheel. The worm wheel has 30 teeth and a pitch diameter of 210 mm. If the pressure angle of the worm is , what is the axial pitch of the worm?

         (a) 7 mm             (b) 22 mm                    (c) 14 mm                    (d) 63 mm