Complete Question 
The complete question is shown on the first uploaded image
Answer:
So the magnetic field on the solenoid 1 is would be 
                   
 
Explanation:
 Now in this question we are given an solenoid and our interest is on the magnetic field on the solenoid 
Now first we will consider the Ampere's law which is mathematically represented as
                         ∮
  Where  is the magnetic filed
 is the magnetic filed 
              ∮ means the close integral 
               is the length element
  is the length element 
                magnetic of permeability of free space
 magnetic of permeability of free space 
                 is the enclosed current
 is the enclosed current 
 Now choosing a current path on a  particular side of the solenoid (as shown on the second uploaded image)  to evaluate the magnetic field
      Where  is the current elements within the enclosed current path
 is the current elements within the enclosed current path 
                   is the number of current elements in that particular enclosed current path.
 is the number of current elements in that particular enclosed current path.
           and L is the length of enclosed path in the direction of the magnetic field as shown on the second uploaded image 
   
So the integral of total  path  ∮ =
 = 
Where  are the length element of each sides of the enclosed path
 are the length element of each sides of the enclosed path 
    Now looking at the first integral we see that  is moving the same direction with magnetic field B  as shown on the third uploaded image
 is moving the same direction with magnetic field B  as shown on the third uploaded image  
  Now for  the direction is perpendicular to the the direction of the magnetic field B so the value of magnetic field for that segment is 0 \
 the direction is perpendicular to the the direction of the magnetic field B so the value of magnetic field for that segment is 0 \
Now for  from the third uploaded image we see that there are no this segment so the value is zero
 from the third uploaded image we see that there are no this segment so the value is zero
 segment is the same as
 segment is the same as  segment so the value of magnetic field on this segment is zero
 segment so the value of magnetic field on this segment is zero 
    Therefore       
                     ∮ =
  =  
              
  Now from Ampere's law  ∮ 
  
 
 Now from the second uploaded image we see that  would now be equal to
 would now be equal to 
                Therefore the equation becomes 
                     
 
Now making B the subject we have
                   
Now   where n is the number of turns per length
 where n is the number of turns per length  
                     So we have 
                             
So the magnetic field on the solenoid 1 is would be 
            