This is a way to introduce the idea of combining like terms by thinking of the variables as objects. For example: instead of 1c + 3c think: 1 chair plus 3 chairs is 4 chairs, so the answer is 4c.
I use Burger Algebra I book by Hold-McDougal. Note: I've created this using their problems on the editable Practice worksheets, and placed them into this format. So by purchasing this, you are paying me for my time in organizing the problems into a way that is easy and manageable for students.