a) Call a four-digit number (xyzt)B in the number system with base B stable if (xyzt)B=(dcba)B−(abcd)B, where a≤b≤c≤d are the digits of (xyzt)B in ascending order. Determine all stable numbers in the number system with base B.b) With assumptions as in a, determine the number of bases B≤1985 such that there exists a stable number with base B. number theory proposednumber theory