1. **State the problem:** Solve the equation $-15 + N = -9$ for $N$. 2. **Formula and rules:** To isolate $N$, add 15 to both sides of the equation to cancel out $-15$ on the left side. 3. **Intermediate work:** $$-15 + N = -9$$ Add 15 to both sides: $$\cancel{-15} + N + 15 = -9 + 15$$ Simplifies to: $$N = 6$$ 4. **Explanation:** Adding 15 to both sides keeps the equation balanced and removes the $-15$ from the left side, leaving $N$ alone. The right side becomes $-9 + 15 = 6$. 5. **Final answer:** $$N = 6$$