Hy Prarthana!!

Yes, it is necessary to have maths as a subject in your 12th standard to be eligible to get BBA course at Saint Xaviers College, Mumbai. You have to clear an entrance test of Saint Xaviers to get a seat in this college. In the entrance test you can expect the questions related to maths also. Thus it is mandatory for you to have maths as a subject with commerce in your 12th standard.

I hope your query is clear now.

good luck!!