getBalance is an instance method. The point of the method is it gives you the balance for a specific Account object, so you you need an instance of Account in order to call getBalance on it. When you call a method prefaced by the class name, that's what is meant by 'static context', it means you're calling a static method on the class.
Technically calling the constructor and calling the getBalance method on the new object, like the other posts show, will work but won't give you any useful data. You need to find out how to get the Account that you want (such as through a database query).
Are you trying to subclass Account? Because the bob method looks a lot like a toString that would look at home in Account. If you are subclassing the Account then you don't need to preface the call to getBalance with
Account., instead you can use
this.getBalance() or just
this is implied).