Answer:

Explanation:
When light passes through a narrow slit, it produces a diffraction pattern on a distant screen, consisting of several bright fringes (constructive interference) alternated with dark fringes (destructive interference).
The formula to calculate the position of the m-th maximum in the diffraction pattern produced in the screen is:

where
y is the distance of the m-th maximum from the central maximum (m = 0)
is the wavelength of light used
D is the distance of the screen from the slit
d is the width of the slit
In this problem, we have:
is the wavelength
D = 62.5 cm = 0.625 m is the distance of the screen
We know that the distance between the third order maximum (m=3) and the central maximum is 1.35 cm (0.0135 m), which means that

For
m = 3
Therefore, rearranging the equation for d, we find the width of the slit:
