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Thank you.
First, you should investigate the format() method of strings, full documentation here: https://docs.python.org/3/library/string.html#formatstrings
Your entire string should be built up using "".format() and you shouldn’t use + at all.
Second, you should look into how to use write_string since at the moment you’re passing in a string of "On" and then attempting to supply the rest of your string as an x position: http://docs.pimoroni.com/scrollphathd/#write-a-text-string
This is a good argument for string format- since your current + concatenated string is so visually busy to parse at a glance, you may not have noticed that comma crept in and made most of your string the second parameter to the function call.