When copying a file to another file, the only thing the method really needs to know are the names of the two files (and maybe the data type). The method does not need to know it is copying inventory data. Name your methods and variables appropriately.
This can be the same when just changing one value. The method only needs to know the value to be added.
When you are writing methods, tried to think if this is a general task or is it specific to the application. If it is a general task that the application needs to do, try to use more generic variable and method names. That way you might be able to reuse the code for a different problem.