How much will it cost?

The going rate for math tutoring in my city is about CAD$30 per hour. (At the present exchange rate that is about USD$27, or EUR 20.) I use this rate to calculate what I charge for a given set of questions.

Sometimes a question comes in an area that I haven't looked at in a while, and I need to refesh my memory. And even in calculus there are sometimes topics or applications that I simply have never seen before, so I need to take a few minutes to learn something new. I don't charge for my learning time, only for the time I have my pen in hand, working on someone's solutions.