In Young's double slit experiment the separation d between the slit is 2mm, the wavelength $\lambda$ of the light used is $5896 \; A^o$ and distance D between the screen and slits is 100 cm. It is found that the angular width of the fringes is $0.20^o$. To increase the fringe angular width to $0.21^o$ ( with same $\lambda$ and D ) the separation between the slits needs to be changed to
