When you declare
difference in your code, you’re saving the results of
((sum(city_price) - sum(country_price)) / sum(country_price)) inside of that variable.
Programmers tend to do that to make their code more readable, so when you
print(difference) afterwards, it’s easier to read.
In more complicated programs, programmers will also tend to break their code into smaller functions, to make it easier to read and debug.