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