Hi aspirant 

You can see the IIT B allotment pdf here:   http://jam.iitb.ac.in/round1.pdf

If you are from general you will have to be in top 20s.Accordingly you have to score marks.

The post given below would be helpful to you.

https://university.careers360.com/articles/jam-cutoff

https://university.careers360.com/articles/jam-result

All the best.