To solve this problem it is necessary to apply the concepts related to the concept of overlap and constructive interference.
For this purpose we have that the constructive interference in waves can be expressed under the function
Where
a = Width of the slit
d = Distance of slit to screen
m = Number of order which represent the number of repetition of the spectrum
Angle between incident rays and scatter planes
At the same time the distance on the screen from the central point, would be
Where y = Represents the distance on the screen from the central point
PART A ) From the previous equation if we arrange to find the angle we have that
PART B) Equation both equations we have
Re-arrange to find a,