Complete Question 
A student locates a double-slit assembly 1.40 m from a reflective screen. The slits are separated by 0.0572 mm.
 (a) Suppose the student aims a beam of yellow light, with a wavelength of 589 nm, toward the slit assembly, and this makes an interference pattern on the screen. What distance (in cm) separates the zeroth-order and first-order bright fringes (a.k.a. maxima)?
(b)
Now suppose that blue light (with
λ = 415 nm)
is used instead. What distance (in cm) will now separate the second-order and fourth-order bright fringes?
Answer:
a
 The distance of separation is  
b
The distance of separation is  
 
Explanation:
From the question we are told that 
      The distance from the screen is  
       The slit separation is 
        The wavelength of the yellow light is  
        
The distance of a fringe from the central maxima is mathematically represented as 
        
Where n is the order of the fringe so the distance of separation between  
    The distance that separates first order from zeroth order bright fringe can be evaluated as 
             
 Substituting values 
           
           
Converting to cm 
             
b
The  wavelength of blue light is  
        So the distance that separates second  order from fourth order bright fringe can be evaluated as 
          
 Substituting values 
         
         
Converting to cm 
             