The conclusion of the book is how things end and how the characters change (or don't change) and the lesson that is learned from the book.
Jessie and Evan somehow lose the money that they each earned. And they also lose Megan's money. They needed to work together to come up with a way to re-pay Megan.
No more war!!
They enter into a Labor Day Contest together and create posters explaining their Lemonade Business ideas. Their winning poster earns them $100 - enough to pay back Megan.
The end of the summer was almost ruined and they almost stayed in a war but together, they made a good situation out of a bad one.
They made lemonade out of lemons!