Two concentric coils of 10 turns each are placed in the same plane. Their radii are 20 cm and 40 cm and carry 0.2 and 0.3 amp. current respectively in opposite directions. The magnetic induction (in Tesla) at the center is

Question

\[\begin {array} {1 1} (1)\;\frac{3}{4} \mu_0 & \quad (2)\;\frac{5}{4} \mu _0 \\ (3)\;\frac{7}{4} \mu _0 & \quad (4)\;\frac{9}{4} \mu _0 \end {array}\]