Priorities problem


I have a custom field called severity it works on a scale from 1 to 4,
where 1 is the highest. Unfortunately my perl scripting is non
existent. What I would like is a scrip oncreate where for example if
severity 1 is chosen that it would set initial priority to 60, final
priority to 100 and due date to +4 hours. I know it’s a big request but
if someone could help it would be very much appreciated.

Thanks in advance,