So far I have done 14 out of 15 questions on the LAST problem set of the semester. I am stuck on one question, and no matter what I try, it wont accept my answer (the problem set is electronic). Here is the problem: "A galvanic cell consists of a Pt cathode inmmersed in a solution containing Fe2+ at 2.15 M and Fe3+ at unknown concentration, as well as a Cu anode immersed in a 2.30 M solution of Cu2+. The cell voltage is 0.09 V. What is the concentration of Fe3+ ions? Enter your answer in M." Since I tried the problem so many times, the computer gave me a hint: "Hint: The platinum is acting as the cathode, and the copper is acting as the anode in this cell. Calculate the Eo for this cell, and given the actual emf, work backwards with the Nernst equation to calculate concentrations. Don't forget to count the number of electrons being transferred." Anytime I ask someone in my class how they did it, I get a generic answer like "my friend did it". PLEASE help me on this, this is the LAST problem set question of the semester!!! Thank you..