Textbook!

Today as usual John opened his math textbook he found a page torn in his textbook. He became very angry and wanted to find the culprit.someone wrote a message on the next page as "8x-16 equals to no value but the unknown no. has value which directs towards the roll no. of culprit". John observed that it was written from coffee .John somehow found the roll no. but was his friend who hated coffee. After a week he found his torn page which again had a message"culprit is the one who's roll no. equal to 8x +16 where the unknown no. has no value." John somehow found his friend's enemy who was a great lover of coffee. Also he had the same roll no as written in the torn page, but this time message written by a normal pen. What is the roll no of the culprit?

Assumption: two different people wrote with different things.