Business rule sends an email when it identifies a "HIGH" in Sevice Call

Hi every one ,

I need your help.

Can you tell me an example of how I can create a business rule that sends an email when it identifies a "high" priority service call only when it meets the following conditions.

1.if the service call is "HIGH" priority and 3 hours have passed since its creation and it has not been closed,

You must send a first email "example1@email.com".

2.if the service call is "HIGH" priority and 4 hours have passed since its creation and it has not been closed,

You must send a first email "example2@email.com"

3. if the service call is "HIGH" priority and 6 hours have passed since its creation and it has not been closed,

You must send a first email "example3@email.com"

Can you help me ?