Adarsh is eleventh from the left end and Naveen is 20th from the right end in a row If they intercha...........

Explanation:

 As Adarsh  position from the left end is 11.
And Naveen position from right end is 20 and after interchanging their positon will be interchanged i.e now Naveen is 11 from left   end and Adarsh is 20 from right end and it  is given that after interchange Adarsh is 15th from left end 
so total persons = (left + right)-1= 15+20-1= 34