Hello, it depends on your definition for line efficiency but, I think this link will help you the most: http://www.onlineclothingstudy.com/2011/09/4-how-to-calculate-efficiency-of.html
Joaquín Ordieres, Arun Aditya Sahay, Mike Tierney ... thank you very much for your feedback. I am writing a teaching case, and have figured this out. I calculated the same for the production line of the company on which I am writing the case.