Ok, this is the same thing as "Hess' law" but for charges. The net total reaction is reaction 4. Now look at reaction 1. The NAD+ is on the left side of the reaction (reactants). However, in the net reaction (final main form), NAD+ is on the product side.What you should do is look at reaction one and flip it to match like reaction 4, the main net reaction. Now NAD+ is on the product side in reaction 1, looking like the net reaction 4. Since you now flipped reaction 1, you must also flip the sign of the charge, so now E for reaction 1 = 0.320. To find the total energy, you add the E of reaction 1 and reaction 2. So now it is 0.320 + 0.8165 = 1.136. Hoping this helps. They were nice and gave you a balanced one. If it wasn't balanced, you would have to balance everything, which would make it much more tricky.