Two concentric circular coils $X$ and $Y$ of radii $16\; cm$ and $10\; cm$ respectively,lie in the same vertical plane containing the north to south direction. Coil $X$ has $20$ turns and carries a current of $16\; A$. Coil $Y$ has $25$ turns and carries a current of $18\; A$. The sense of the current in $X$ is anticlockwise,and clockwise in $Y$,for an observer looking at the coils facing west. Give the magnitude and direction of the net magnetic field due to the coils at their centre.

• A
  $5.34 \times 10^{-3}\; T$ (towards North)
• B
  $7.24 \times 10^{-3}\; T$ (towards West)
• C
  $1.57 \times 10^{-3}\; T$ (towards West)
• D
  $1.57 \times 10^{-3}\; T$ (towards East)