Originally Posted by

**mr fantastic** You were asked in post #2: Are you allowed to use calculus? Please answer this question.

And if you have not learned calculus then you should not be asking questions about a solution that uses calculus. (And more to the point, if you are asking the original question at another website and getting replies you don't understand, then **that** website is the place where you should be asking your question).

You have been given a non-calculus method in earlier posts (and people have spent their time giving it to you). If this is not the method you want to use, please say so. Otherwise, use the method given in those earlier posts and ask questions about **it** if you're still stuck.