In your notebook, set up the following addition using a vertical format and find the sum of the given polynomials.
a - b + c, b - c + d, and c - d + e

A - b + c, b  - c + d, and c - d + e  ; in a vertical form and add them up.
 
We must ensure that similar letters are under the same column.

a - b + c
   + b -  c  + d
              c  -  d  + e
a + 0 + c + 0 + e

a + c + e is the sum of the given polynomials.

The other letters cancel themselves out because they have different signs.

If you set up the addition using a vertical format and find the sum of  the given polynomials, the answer would be: a + c + e