Hi

According to the official link

https://mathematics.nmims.edu/docs/B.Sc%20Mathematics%20(Honours)%20-%202020%20Admission%20Info.pdf this could mean either that your rank in the merit list is 9 (if by merit number you mean the number in merit list). If this is not the case, it could also mean that this is your merit score, which is calculated in the above link.

Hope this helps!