[jameshart]

The question doesn't ask you to find a solution - it says "what combinations" can you find - plural.

You're not done when you've found one. Are you sure you can't buy ten yoyos, three cars and a pinwheel and hit the number too?

[novia]

If you keep reading it asks if your solution was the only possible solution. This implies that you only have to give one solution and prove that there are no other solutions (very difficult) or find two solutions to show that there could be many more than just one.

When the son said that some people in the class got the problem exactly right, I doubt they spit out all 279 combinations.

[jameshart]

All of which is just more evidence in the column of 'this is a terrible question, ill-posed, and pedagogically invalid'