Hi - I'm not good with formulae...

I have a number field - Support, 
I'd like a new formula field - 
if value is <10, "low"
if value 10-18 "high"
if value >18 "incomplete"

I can see how to do an if based on <10, going low/high... but needing the 3rd option has got me stuck.

Hi - I'm not good with formulae...

I have a number field - Support, 
I'd like a new formula field - 
if value is <10, "low"
if value 10-18 "high"
if value >18 "incomplete"

I can see how to do an if based on <10, going low/high... but needing the 3rd option has got me stuck.