A toroid made of CRGO has an inner diameter of 10 cm and an outer diameter of 14 cm. The thickness of the toroid is 2 cm. 200 turns of copper wire is wound on the core. \( \mu_0 = 4\pi \times 10^{-7} \, \text{H/m} \) and \( \mu_r \) of CRGO is 3000. When a current of 5 mA flows through the winding, the flux density in the core in millitesla is \(\underline{\hspace{2cm}}\).