1 > What's the best way/query to calculate the SLA for a P1/P2 ticket?....2 > Need a query to monitor SLA response in Real Time?

Hi
This is my first post and my knowledge of Service Now is slightly better than a 6 year old :)
I would like to:
1 > Understand the best query to calculate the SLA for a P1/P2 ticket?
2 > Need a foolproof query to monitor SLA response in Real Time?

Much appreciate a quick response.

Thanks
Praveen Vasudevan