1. **Solve for x in the equation 4x - 9 = -21.** 2. Start by isolating the term with x. Add 9 to both sides: $$4x - 9 + 9 = -21 + 9$$ $$4x = -12$$ 3. Now divide both sides by 4 to solve for x: $$\cancel{4}x \div \cancel{4} = \frac{-12}{4}$$ $$x = -3$$ 4. The solution is $x = -3$. This means when $x$ is $-3$, the original equation holds true. Final answer: $x = -3$