A rectangular coil of area  5.0×10−4m2 and 60 turns is pivoted about one of its vertical sides. Then coil is in a radial horizontal field of 90 G (radial here means the field lines are in the plane of the coil for any rotation).  The torsional constant of hair spring connected to the coil if a current of 2.0 mA produces an angular deflection of  is  180 is x×10−8Nm/degree