You can't combine oranges with apples, just oranges with oranges and apples with apples. Think about it that way.
In this specific problem, the only thing you need to do is add those numbers together as they are like terms (both have y), you'd get 37y.
With a problem like 2 + 5x + 3 + x, you'd have to identify which are like terms and which aren't. The x's go together, and 2 and 3 go together. The result would be 5 + 6x, since you can't combine x and 5.
Hope I helped! :)