Redmine

Hi,
I need help with a plugin , where I need to set a due date by issue type priorities. I have 4 priorities - A, B, C, D. A is very difficult bug - needs to be removed for one day from its report, D is an easy bug and needs to be removed within a week. Can someone help me with this? Thanks

examples:

1. start date is 2015/8/11 and priority is A => due date automatically set on 2015/8/12
2. start date is 2015/8/11 and priority is B => due date automatically set on 2015/8/15
3. start date is 2015/8/11 and priority is D => due date automatically set on 2015/8/19