Which expression best represents the difference between triple a number and double a number?

You start of with a number, ( this number can be any number) so think of it as an unknown number. the  number shall be denoted as x so you have x you want triple the number 3x you also want to double the number 2x you want the difference so you subtract these two terms 3x-2x

If cheese is $4.40 per kilogram, you should pay .88