How to translate "9 less than three times a number" into an algebraic expression?

"9 less than" indicates that you are taking 9 away from something.
"9 less than 12 is 3" would be written as ${\displaystyle 12-9=3}$
The "something" in this instance is three times an undetermined number.
Call the number ${\displaystyle x}$
Three times the number is ${\displaystyle 3\times x=3x}$
"9 less than this" is written as ${\displaystyle 3x-9}$