Hello Aspirant!
According to the last year's data available on the official website, to get admission in BMS in St. Xavier's College, Kolkata (as BBA course is not mentioned on the college website), you need to first apply online after declaration of the board results. The application portal usually opens by the end of May. But this year, due to COVID-19 outbreak, there can be changes.

Pure Mathematics/Buisness Mathematics/Statistics at (10+2) level is compulsory for this course. An aggregate of 60% marks is essential for taking honours in BMS, with passing individually in all the subjects from a recognized board.
You will have to appear for an entrance examination of one hour duration comprising of MCQs of 50 marks.
50% weightage will be given to your Class 12th aggregate percentage and the rest 50% weightage will be for your entrance scores out of 50 marks.

Selection list will be published on the college official website : https://www.sxccal.edu

Hope this answer will help you.

Hello Aspirant

For securing an admission you will need to pass you class 12th exams with minimum 60% score. The passing of English language is compulsory and then the college will take an interview and candidates who pass this will secure the admission.