Books are identified by an International Standard Book Number (ISBN), a 10-digit code x1 x2...x10, assigned by the publisher. These 10 digits consist of blocks identifying the language, the publisher, the number assigned to the book by its publishing company, and finally, a 1-digit check digit that is either a digit or the letter X (used to represent 10). This check digit is selected so that \sum_{i=1}^{10} ix_i \equiv 0 \text{ mod } 11 and is used to detect errors in individual digits and transposition of digits. a. The ISBN for a book is 1-32-794182- Q} where Q is the check digit. What is Q?
b. The ISBN of another book is 2-429-39M18-6. Find the digit M.