Two $50-$mm$-$wide slits spaced $0\mathrm{.}40$ mmmm apart are illuminated by blue laser light with a wavelength of $450$ nmnm$.$ The interference pattern is observed on a screen $2\mathrm{.}0$ mm behind the slits. How many bright fringes are seen in the central maximum that spans the distance between the first missing order on one side and the first missing order on the other side? What is the width $($in mmmm$)$ of the central maximum on a screen $1\mathrm{.}8$ mm behind the slit?