A loop ABCDA, carrying current $$I = 12$$ A, is placed in a plane, consists of two semi-circular segments of radius $$R_1 = 6\pi$$ m and $$R_2 = 4\pi$$ m. The magnitude of the resultant magnetic field at center O is $$k \times 10^{-7}$$ T. The value of k is __________.
(Given $$\mu_0 = 4\pi \times 10^{-7}$$ Tm A$$^{-1}$$)