The sum of twice a number and 5 is at most 15. what are the possible values for the number

I would start by writing this as an equation. 2n+5 is less than or equal to 15.
subtract the five from both sides to get 2n is less than or equal to 10. Divide both sides by 2 and you get n is less than or equal to 5, this is your answer.

No because if you do the higher number minus the lower number you will get a positive. if you do it the other way around you will get a negative number