The xy-plane serves as the interface between two different media. Medium 1 (z < 0) is filled with a material whose mu_r = 6, and medium 2 (z > 0) is filled with a material whose mu_r = 4. If the interface carries current (1/mu₀) aᵧ mA/m, and B₂ = 5a_x + 8a_z m Wb/m², find H₁ and B₁.