Calculated field on decimal field for text

I would like to create a new calculated textfield field based on business_hours field (decimal type) that returns a value of "Met" or "Missed"

for when the business_hours field is not empty

based on 

if the field CaseType = RFQ and business_hours is less than or equal to 4 hours

or

if the CaseType is equal to (RFI or NCO or ORD) and business_hours is less than or equal to 8 hours

"Met"

Else

"Missed"