Validation Rule: If "Contact" field and "Report Broker" field have been updated then "Report Level" field must be updated/or have input.

Basically what the title says. Validation Rule: If "Contact" field and "Report Broker" field have been updated then "Report Level" field must be updated/or have input. I've heard the use of If change statements would be used, but looking for more feedback on the topic of what it might look like. 

Thanks!

Nick Engstrand