Mr. Denis has 5 goats with the average weight 36 kg while Mr. Joppy has 5 goats with the average weight 34 kg. If they exchange one of their goats so that their overall average weight is equal, what is the weight difference of their switched goats? I only know that Mr. Denis' goats' total weight is 180 kg and Mr. Joppy's is 170 kg. How to do it from there?