Hii Aradhya..

Delhi University consists of lots of college under it and some college specify certain rules for calculating best of four marks while others do not. Thus I would suggest you to check the cutoff criteria of marks of the colleges specifically before coming on any decision because that policy may vary from college to college.

Some college may want you to include your accountancy marks in best of four for admission in Bcom where is other college do not specify the subject to be included by calculating the best of four marks. Thus I will suggest you to check it on the official website of Delhi University for the criteria of calculating best of four marks as it is given along with the cutoff percentage marks.

Hope it helps. 

Best of luck for your future.