Q. A person uses the base x for his number system, where x  ≤ 10. A student had to add two-digit numbers. None of the digits was 0. By oversight, he reversed the digits of both the numbers and added them. He later found that the difference between his answer and the correct answer was $(84)_­­10. If this value is the maximum possible for x, then what is the value of x.

1. 9
2. 8
3. 7
4. 6