1. **State the problem:** We need to find the missing transaction $N$ on Dec 1 such that the account balance becomes zero after all transactions. 2. **List all transactions:** - Dec 1: $N$, +500, +330, -2000 - Dec 2: +2000, -1000, -1040, -200, -115 3. **Set up the equation:** The sum of all transactions must equal zero: $$N + 500 + 330 - 2000 + 2000 - 1000 - 1040 - 200 - 115 = 0$$ 4. **Simplify the constants:** $$500 + 330 - 2000 + 2000 - 1000 - 1040 - 200 - 115 = (500 + 330) + (-2000 + 2000) + (-1000 - 1040 - 200 - 115)$$ $$= 830 + 0 + (-2355) = 830 - 2355 = -1525$$ 5. **Solve for $N$:** $$N - 1525 = 0 \implies N = 1525$$ 6. **Interpretation:** The missing transaction $N$ is a deposit of 1525 to balance the account to zero. **Final answer:** $$\boxed{1525}$$