cinder

My teacher gave us a few homework questions regarding on arranging oxidizing agents on their strengths. I can tell if it's strong or weak if it's on a table... However, there's a question where we have to arrange it based on the voltage it produced?? For example: Reduction reaction Oxidation reaction Resulting voltage Cu+2 + e- --> Cu+ Pb ---> Pb+2 + 2e- 0.11V Cu+2 + e- --> Cu+ Ni ---> Ni+2 + 2e- 0.05V Cu+2 + e- --> Cu+ Fe ---> Fe+2 + 2e- 0.09V Can someone explain to me how to do it?? Thank you!