1. **State the problem:** Solve the equation $5X - 10 = -15$ for $X$. 2. **Add 10 to both sides to isolate the term with $X$:** $$5X - 10 + 10 = -15 + 10$$ $$5X = -5$$ 3. **Divide both sides by 5 to solve for $X$:** $$\frac{\cancel{5}X}{\cancel{5}} = \frac{-5}{5}$$ $$X = -1$$ 4. **Final answer:** $X = -1$. This means that when $X$ is $-1$, the original equation holds true.