Please solve with steps

Monochromatic light is incident on a sheet with three equally spaced slits a distance, d, apart. (a) Use the concept of phasors to show that the positions of the interference minima on a screen a large distance L away from the sheet that has the three equally spaced slits (spacing d, with d > > >) are given approximately by ym = mAL/3d where m = 1, 2, 4, 5, 7, 8, 10, .. . that is, m is not a multiple of 3. (b) For a screen distance of 1.00 m, a light wavelength of 500 nm, and a source spacing of 0.100 mm, calculate the width of the principal interference maxima for three sources. (c) Draw a figure of the interference pattern expected for the situation described above and indicate the maxima and minima for m=1 to 5