Can someone help me with Geometry (with a little bit of trigonometry thrown in)?

So we have a regular pentagon (PQRST) with center (O). the apothem (which is not given) goes from O to point X (which is located in between points P and Q). I have found angle POQ and angle POX, but now I am asked to find the length of O to X, the perimeter, and the area. The examples in the book tell me to use trigonometry (sine, cosine, and tangent) but I'm completely stumped. I already got the answer from the back of the book, but I just want to know how to do it!