A surface current \( \mathbf{K} = 100 \, \hat{x} \, \text{A/m} \) flows on the surface \( z = 0 \), which separates two media with magnetic permeabilities \( \mu_1 \) and \( \mu_2 \) as shown in the figure. If the magnetic field in the region 1 is \( \mathbf{B_1} = 4 \hat{x} - 6 \hat{y} + 2 \hat{z} \, \text{mT} \), then the magnitude of the normal component of \( \mathbf{B_2} \) will be ............. mT.
