In a Fresnel's biprism experiment,fringes are obtained in the focal plane of an eyepiece at a distance of $1 \ m$ from the slit. $A$ convex lens is placed between the biprism and the eyepiece. The images of the slit are formed at two positions of the lens. The distances between the two images of the slit at these two positions are $4.05 \times 10^{-3} \ m$ and $2.9 \times 10^{-3} \ m$ respectively. Calculate the distance between the slits.

• A
  $3.43 \times 10^{-3} \ m$
• B
  $3.75 \times 10^{-3} \ m$
• C
  $1.23 \times 10^{-4} \ m$
• D
  $2.33 \times 10^{-3} \ m$