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I think you just have to figure out the charges on your own based off of other information. In the example Lavelle gave in class, he used the reaction between MnO4- and Fe+2. On the products side of the reaction, you see that MnO4- has a net charge of -1, and since you know that O has a charge of -2, you can calculate that the Mn ion has a charge of +7. There are some that you just have to know (e.g. O having a -2 charge), and others you will have to calculate.
There aren't really "rules" for redox reactions, but they make use of the typical oxidation states of the elements. When calculating the charge changes, we won't be given them in the question. Instead, we'll easily be able to find them from the periodic table, or memory as we've used these charges many times before.
A lot of the time you can also look on the periodic table for charges. For example, elements in column one have 1+ charge, and elements in the halide column usually have a charge of 1-. As you go further in to the middle of the periodic table it becomes less predictable, but you can usually figure it out, knowing that oxygen always reflects 2- charge.
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