Permissions in folder owned by group www-data

I run apache2 webserver on Debian 9 and root of that web is located in /srv/www/, I am logged as user tomsk, problem is that I don't have a permissions in /srv/www/ because it is owned by www-data group.

As far as I know, www-data has only read permissions in that folder so I shouldn't give a write permission for group www-data in that folder.

Let's say that I have a group named developers and I am a member of that group. What I have to do to give a permissions for group developers in folder /srv/www/, without affecting a apache2's default www-data group?

EDIT: Shouln't it be 2470? Because user (www-data) can only read, group (developers) can do anything and others cannot do anything.