1. **State the problem:** Solve the equation $$-10p + 9p = 12$$ for the variable $p$. 2. **Combine like terms:** The terms $-10p$ and $9p$ are like terms because they both contain $p$. Combine them: $$-10p + 9p = (-10 + 9)p = -1p$$ So the equation becomes: $$-1p = 12$$ 3. **Isolate the variable:** To solve for $p$, divide both sides of the equation by $-1$: $$\frac{-1p}{\cancel{-1}} = \frac{12}{\cancel{-1}}$$ This simplifies to: $$p = -12$$ 4. **Final answer:** The solution to the equation is: $$p = -12$$