Which is the best college in Kolkata for BCA? I am expecting around 75% and 80 marks in maths in 12th boards.

Try visiting UEM Kolkata to get aware of eligibility options of BCA: https://www.shiksha.com/university/university-of-engineering-and-management-kolkata-47398/courses/bca-bc

As you have listed your expected marks still you need to go for a separate exam to do BCA from a good college. I suggest you go for UEM-Kolkata to be one of the best to fulfil your desire of pursuing BCA from best one in West Bengal. Just go through the link and help yourself with relevant informati