If two students, Mark and Lisa, interchange their seats, Mark is now 5th from the top and Lisa is 10th from the bottom. How many students are there in total?
In a code language, 'COW' is represented as '3719'. If 'C' is 3, 'O' is 15, and 'W' is 23, what is the code for 'PIG' where 'P' is 16, 'I' is 9, and 'G' is 7?