All three windows are the same size.
A has 10 complete waves visible through the window. B has 3, and C has 4. 
So A must have the smallest wavelengths.
 
        
                    
             
        
        
        
Answer:
m = 3.91 kg
Explanation:
Given that,
Mass of the object, m = 3.74 kg
Stretching in the spring, x = 0.0161 m
The frequency of vibration, f = 3.84 Hz
When the object is suspended, the gravitational force is balanced by the spring force as :



k = 2276.52 N/m
The frequency of vibration is given by :



m = 3.91 kg
So, the mass of the object is 3.91 kg. Hence, this is the required solution.
 
        
             
        
        
        
C
Explanation:
 that's just what I learned in school
 
        
                    
             
        
        
        
The answere is No pain, no gain