Hi Sonali, 

The calculation of best four score depends on the course you want to take admission in, as different courses have different requirements of subjects. Check this Information Bulletin and I hope you'd find the answers you are seeking.

https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.du.ac.in/du/uploads/Admissions/2018/UG/UG_Bulletin2018Final.pdf&ved=2ahUKEwjkpq-xv73iAhXRQ3wKHV7aBH4QFjABegQIAxAB&usg=AOvVaw36w8zqM0o1ZYhySIHjGjRu