Part $($a$)$

Find the angle $($in degrees$)$ between the first minima for the two sodium vapor lines, when they fall upon a single slit with a width of $1\mathrm{.}9$ m$.$

$$ Part $($b$)$

What is the distance in mm between these minima if the diffraction pattern falls on a screen $0\mathrm{.}95$ m from the slit?

yb $-$ ya