$)$ Suppose you set up a two$-$slit interference experiment using a $1000$nm laser. a$)$ The screen is set up $2$m from the two slits. Near the center of the interference pattern, the successive bright $($or dark$)$ fringes are located $5$mm apart. What is the separation of the slits? b$)$ There are exactly $7$ bright fringes within the first diffraction spot. What is the width of the slits?