When I tried to do it I couldn't even get 3 and 4 in place! I was horrified and quit the game. But I tried again today and had no problem doing the whole thing, lickety-split. You just make a train with your numbers and then choo-choo them into place. Simple.
So I guess I'm not getting Alzheimers. Weird how it came back to me. It's like riding a bike -- something you don't forget. My brain recalled the choo-choo move and that was that. I guess the game is about spatial relationships and keeping a certain number of things in mind at the same time. Or something. Anyway, it's fun. Did you play "15" -- as it was called in the day -- when you were a kid?
By the by, the free app sucked but the 99-cent one worked great.