3. divide top and bottom by and let x go to infinity (if thats the limit being asked) bearing in mind in the limit x goes to infinity
5. just plug x=5 into the equation
What you have written for 3 makes no sense. In order to talk about a "limit" you must have a limit as x goes to some valule. Krahl assumed you were talking about the limit as x goes to infinity. Is that correct?
For both 4 and 5, just plug the number into the formula.