First Grade Tries to Challenge Us!

So Mrs. Runyan's friend, Cohen, came to deliver a math problem to our class today. The first graders are working on writing their own problems. Here it is:

Rosa went to the store to buy 4 toy cars. Max bought 6 toy cars. How many do they have in all?

Well, take a look below! I only had 4 who got stumped on it, so we're asking for a harder question!