You may want to review adding two polynomials first.

To add more than two polynomials, you just go one addition at a time. First add the first two, then add the result to the next one, and so on until you finish. (Actually, you can do it in any order; but if you do it in this one then you're less likely to forget one of the polynomials.)

It's the same thing if some of the operations are subtractions;
just go from right to left. With subtraction, though,
you *have* to do it in that order; otherwise you'll get the
wrong answer.