The twins Maxim & Minerva independently replaced the letters in the word KANGAROO upon the following rules:
1. Similar letters are replaced by the same digit
2. The resulting 8-digit number must be divisible by 11.
3. Maxim had to choose the maximal qualifying number, Minerva - the minimal.

Comparing their correct answers they've found out that a certain letter in the word KANGAROO was replaced by the same digit in their independent answers.

Specify WHAT letter and explain WHY.