Two questions, please. I have provided diagrams!

1. Find the measurement of <a, <b, <c, and <d. Explain your reasoning in each case.

http://img.photobucket.com/albums/v1...en/math001.jpg

2. In the diagram, tangents have been drawn from P to the circles. If O is the center of the smaller circle, find the exact value of PO. Explain your reasoning.

http://img.photobucket.com/albums/v1...en/math002.jpg

If you could elaborate on how to come to the answer, that'd be great!