Hi,

First of all you have to know the meaning of the following codes

GM : General Merit

3B :

1. 3BG :     3B General
2. 3BK :     3B Kannada
3. 3BR :     3B Rural

As you belong to 3B category you may select among the three options under 3B category. Now you have to take help of your parents to ensure whether you belong to 3BG or some other category. You may find some information in your caste certificate also. Make sure you select the correct category in application form.