1. **State the problem:** Simplify the expression $25x + 3y + 7z - 10x + 5y + 2z + 18$. 2. **Identify like terms:** Like terms are terms that have the same variable raised to the same power. Here, $25x$ and $-10x$ are like terms, $3y$ and $5y$ are like terms, $7z$ and $2z$ are like terms, and $18$ is a constant. 3. **Combine like terms:** - Combine $25x$ and $-10x$: $$25x - 10x = (25 - 10)x = 15x$$ - Combine $3y$ and $5y$: $$3y + 5y = (3 + 5)y = 8y$$ - Combine $7z$ and $2z$: $$7z + 2z = (7 + 2)z = 9z$$ - The constant $18$ remains as is. 4. **Write the simplified expression:** $$15x + 8y + 9z + 18$$ This is the simplified form of the given expression.