Array e of ints contains the digits of a number without its check digit. write code to calculate the check digit for this number and store it in checkdigit. the check digit should be such that, if it were inserted after the last digit of e, the result would be the digit array of a number that is valid according to the luhn algorithm.

Suppose you are an ad-serving company and you maintain a log of cookie data for ads you serve to the web pages for a particular vendor (say amazon). a. how can you use this data to determine which are the best ads? b. how can you use this data to determine which are the best ad formats? c. how could you records of past ads and ad clicks to determine which ads to send to a given ip address? d. how could you use this data to determine how well the technique you used in your answer to part c was working? e. how could you use this data to determine that a given ip address is used by more than one person? f. how does having this data give you a competitive advantage vis-à-vis other ad-serving companies?