Well, we bought Poulsen for 9.75m eur while Milan bought Ronaldinho for 22m eur, not 18m eur. Only here the difference is 12.25m eur.
We'll pay 6m eur for Poulsen's wages this year (including taxes) while Milan will pay 13m eur for Dinho's wages, including taxes. Here the difference is 7m eur.
12.25+7 = 19.25m eur, only for this year.
Ronaldinho signed 3 years contract. Milan will have to pay 39m eur only for his wages in these three years. Plus the 22m transfer fee, you get the number 61m eur for 3 years.
For the same three years Juve will pay 18m eur for Poulsen's wages +9.75 his transfer fee = 27.75m eur.
The difference for the 3 years is 33.25m eur.
Of course, it's Ronaldinho we're talking about and he may bring even more money than what Milan spent for him.
99% Ronaldinho will turn out to be a better transfer than Poulsen, i'm not denying that.
But people should know that the difference between Dinho and Poulsen wasn't 8m eur only.