Hey Vishal

While calculating your best of four percentage, 1 language and 3 core subjects are taken into consideration in order to decide the eligibility criteria for a specific course.

You can't add another subject which not listed under the list B prescribed by the University as an elective subject.

To know more about how to calculate best of four score, kindly check the link below -

https://www.google.com/amp/s/university.careers360.com/articles/delhi-university-admissions-how-calculate-best-of-four-marks/amp

Thanks