Find H in a material where (a) r = 4.2, there are 2.7 10 29

Find H in a material where

(a) μ_r = 4.2, there are 2.7 × 10²⁹ atoms/m³, and each atom has a dipole moment of 2.6 × 10⁻³⁰a_y A·m²;

(b) M = 270a_z A/m and μ = 2μ H/m;

(c) χ_m = 0.7 and B = 2a_z T.

(d) Find M in a material where bound surface current densities of 12a_z A/m and −9a_z A/m exist at ρ = 0.3 m and 0.4 m, respectively.