A magnetizing field of 1800 A/m produces a magnetic flux of 3 x 10⁻³ Wb in an iron bar of cross-sectional area 0.2 cm². Calculate the permeability.

A. 1.5 x 10³ H/m
B. 7.5 x 10³ H/m
C. 9 x 10³ H/m
D. 1.8 x 10³ H/m