PN, I'd have to say your answer does not solve the puzzle.
You say draw the line x=100.
That's already seven lines before you start - yours makes eight.
If you can assume some existing indication of "100", you don't even
have to draw one line; just point to the "100". So it seems clear that
you can't assume an existing "100" indicator.
Take a blank sheet of paper and create "100" with a single line.