Find the values of the letters in the following and give reasons for the steps involved.
2 A B

• A B 1

---

B 1 8

If B + 1 = 8, then B has to be 7. Now we have A + 7 has to end with 1, so it has to be 11, ∴ A has to be 4. Then, 2 + A + 1 (carry over) = B. Thus, A = 4, B = 7