Collecting Like Terms

Like terms have exactly the same variable part. $3x$ and $5x$ are like terms; $3x$ and $3y$ are not, and neither are $4x$ and $4x^2$. You can only add or subtract like terms — just add their number parts (the coefficients) and keep the variable:

To simplify a longer expression, gather each family of like terms:

The $6x$ and the $8$ are unlike, so $6x + 8$ is as far as it simplifies.

Worked example. Simplify $9y - 4y + 2y$.

All like terms: $9 - 4 + 2 = 7$, so the answer is $7y$.