Continuity mistake: When Auggie and Jack are running from the bullies Jack gets closer to one of the trees between shots.
Continuity mistake: When Amos, Henry, and Miles are fighting off the bullies Amos is hanging one of them over his shoulders. In the next shot Auggie is grabbing at the bullies' legs which are suddenly on the ground.
Answer: Yes, the solution given is wrong, it should be (x=-4, y=4). Glad I'm not the only one noticing that. Actually that's how I found this page :)