1. **State the problem:** We need to find the value of the expression $6 - 3x$ when $x = -4$. 2. **Write the expression:** The expression is $6 - 3x$. 3. **Substitute the value of $x$:** Replace $x$ with $-4$ in the expression: $$6 - 3(-4)$$ 4. **Simplify the expression:** Multiply $-3$ by $-4$: $$6 - \cancel{3} \times (-\cancel{4}) = 6 + 12$$ 5. **Add the numbers:** $$6 + 12 = 18$$ **Final answer:** When $x = -4$, the value of $6 - 3x$ is $18$.