Consider a web system for online shopping that will generate an ID for each order. The order ID is a sequence of 7 characters where each char- acter could be either one of the 26 upper case English letters (A to Z) or one of the 10 digits (0 to 9). (a) How many possible order IDs are there? (b) How many possible order IDs are there if the leftmost character must be a digit and no two consecutive characters are the same? (E.g. 3ABA3C6 is valid. C3ARX7B and 3ARRX7B are invalid) (c) How many possible order IDs are there if characters must alternative between a letter and a digit? (E.g. A3R4B7Q and 4V7X3V7 are valid, B7XB4Q3 is invalid)