Hi

Your GMR is considered for wbjee and not your category rank.

This is very difficult to predict because cut off keeps changing every year depending upon a number of factors like

--------) number of students that appeared in the WBJEE exam

--------)difficulty level of the WBJEE examination

--------)Kind of marks obtained by the students in the WBJEE exam

--------) number of students from different categories

--------) seats available for different branches etc

But yes,

With your 31000  rank being from obc-b , category,

On the basis of analysis of past years wbjee cut off data , yes you have good chances in government engineering college.

For example,

In 2020 , in 3rd round of wbjee, 44396   gmr rank for obc-b category got a government engineering college and it was for  Cooch Behar Government Engineering College, Civil Engineering

As per 2020 cut off available at Official website :- https://admissions.nic.in/wbjeebcouns2019/wbjeebcouns2019/orcr/PrevYearORCR.aspx

To have a personalised report on your chances of getting a college you can go through our WBJEE college predictor, it will give you complete list of colleges which you can get on the basis of the category you belong to,  your , your gender etc the link for  WBJEE  college predictor is provided below

Thankyou