Answer:
Explanation:
The relationship between angle and wavelength for maxima and minima in Young's double slit experiment is given by
For constructive interference

For Destructive interference

where 

m=order of maxima and minima
for second order maxima i.e. 
For smallest separation taking 



C. Quarts watches is the correct answer
ANSWER IS A)
THE SPEED IS 25 M/S FOR BOTH PEOPLE