This is a Fraunhofer single slit experiment, where the light passing through the slit produces an interference pattern on the screen, and where the dark bands (minima of diffraction) are located at a distance of

from the center of the pattern. In the formula, m is the order of the minimum,

the wavelenght,

the distance of the screen from the slit and

the width of the slit.
In our problem, the distance of the first-order band (m=1) is

. The distance of the screen is D=86 cm while the wavelength is

. Using these data and re-arranging the formula, we can find a, the width of the slit:
Sound waves....................................
Answer:
44.4 m/s
Explanation:
d = 80 m, t = 1.8 s, find v
d = v*t
v = d/t = 80/1.8 = 44.4 m/s
The answer of this question would be D