So if you find the charge on one of the capacitors, you've found the charge on all of the capacitors. Solving for the charge, we get that the charge stored on this equivalent capacitor is 18 coulombs.
If you add up the voltages across the components in any single-loop circuit like this, the sum of the voltages is always going to equal the voltage of the battery. These voltages have to add up to the voltage of the battery. But that's easy now because the charge on each of the individual capacitors in series is going to be the same as the charge on the equivalent capacitor. We'll use the same process as before. Well, there's a trick we can use when dealing with situations like this. This time, let's say you had four capacitors hooked up in series to a volt battery.