a$)$Find the angle between the first minima for the two sodium vapor lines. which have wavelengths of $537\mathrm{.}9$ and $565\mathrm{.}8$ nm$,$ when they fall upon a single slit of width $2\mathrm{.}02$E$-6$ m$.$

b$)$ What is the distance between these minima if the diffraction pattern falls on a screen $2\mathrm{.}78$m from the slit? m