Challenges are really easy in this game, especially with the hint system. Hint 3 tells you everything you need to know. There is no achievement for using no hints so you might as well abuse this feature if you're not sure how to complete a challenge or can't figure out any other solution. Hints refresh each time you complete a challenge, so when you use a hint again, it'll be telling you how to do the challenge with a different solution.
To use hints press at the Challenges section when you highlight the challenge you want to do. You'll have to wait several seconds between using hints.