Colleges in Kolkata

Yes, you have to apply for the entrance exam only.

Hi,
If you're having a BSc degree in mathematics, only then will you get admission into M.Sc Mathematics as maths is the main subject and is required in B.Sc final year, if a candidate wants to do M.Sc in the same.
In addition, you must first check with the cutoff percentage as yours is a bit low.

Yes you can easily take admission in M.Sc. But you have to be a graduate student or qualified graduation.

The given fees for that course is:
Bachelor of Business Administration [BBA]
3 year (s), Full Time
Total Fees Rs. 1,86,000
For more information, please check the website:
https://www.google.co.in/url?sa=t&source=web&rct=j&url=http://www.sxccal.edu/admissions/SXCAdmission2014/UG2014/fees.htm&ved=0ahUKEwj_x92dtsbUAhUYSI8KHUY8CfEQFggpMAE&usg=AFQjCNH8m6YQqFIlM_Gte4lkicESHl7ibQ&sig2=2Sm83o-Vuku-GzDdZPSVJw

You can always go for M.Com course. It's a great course that can get you to the postgraduate degree and stand out above grads. However, if you are looking for a distinct career option based on a professional qualification for growth, consider doing a professional course.