Two short bar magnets of length 1 cm each have magnetic moments $1.20\; Am^2$ and $1.00\; Am^2$ respectively. They are placed on a horizontal table parallel to each other with their N poles pointing towards the South. They have a common magnetic equator and are separated by a distance of 20.0 cm. The value of the resultant horizontal magnetic induction at the mid - point O of the line joining their centres is close to (Horizontal component of earth’s magnetic induction is $3.6 \times 10^{–5} Wb/m^2$)
( A ) $3.6 \times 10^{-4} Wb/m^2$
( B ) $2.56 \times 10^{-4} Wb/m^2$
( C ) $5.80 \times 10^{-4} Wb/m^2$
( D ) $3.50 \times 10^{-4} Wb/m^2$