For certain dynamometer ammeter, the mutual inductance M varies with deflection θ (expressed in degrees) as M = -5 cos (θ + 30°) mH. If the deflection torque produced by 60 mA current is 18 × 10-6 N.m, the deflection of the instrument is _________(in degrees)
1
45°
2
60°
3
30°
4
0°