Answer:0.369 m
Step-by-step explanation:
Given
Distance between slit and screen is 
Wavelength 
Angle between zeroth order bright fringe and Fourth-order bright fringe is 
let distance between the slits be d
Distance of n th bright fringe From central Fringe is given by

Also 



Let the number be x.
Therefore, by the problem
x/6-(-3) = 12
or, x/6+3 = 12
or, x/6 = 12-3
or, x/6 = 9
or, x = 9 × 6
or, x = 54
The number is 54.
step 2 would be 10
step 4 would be 10x-x = 9x =7
x = 7/9
The answer is c because of y=mx+b