This is quite a tricky question, I don't blame you for struggling with it. The trick is to first gather as much information as possible using the properties of a circle, its tangent and its radius first, then look over all the clues you have and see how many connections you can make and where you can substitute any equations.

Hopefully this solution is clear enough for you to follow logically. If you find any of these steps to be unclear, feel free to contact me!