Equation Balancing MEGA PRACTICE

Looking to practice some equation balancing? I've got a mega-sheet of 214 practice equations on it:
https://docs.google.com/document/u/1/d/1v52Nyx6o00ABjoISuZHLujTHJGbqAriGw4-9LhqXbhM/pub

Looks pretty lame, right? No answers to any of the balancing equations? Highlight the whole line and the coefficients magically pop out (use Ctrl-A to highlight the whole page) Ok, its not MAGIC, per se, but still cool.

Here's how I got it to work - when you publish a Google Doc, you can't change the color of the background. It always just goes to a white page. HOWEVER, if you create a table, you can set the background of the table. So I set the coefficients to be the same color as the background, so they are hidden until you highlight it.

The REAL fun was selecting every single coefficient at the same time with a regular expression in Word and then exporting it to Google Docs, but I'll save that for anyone who cares. :)