Calculate a date in a form


I have two fields in a form: Request Type and Due Date

I need to calculate (or perform a vlookup to another sheet) if the date that is chosen dfalls within an agreed timeframe based on the Request Type that is chosen.

i.e. if Request Type = Email AND Due Date is less than 5 days from the submisson date then show a SLA warning field/message.

So far I have dran a blank.