Star Trek / 47:
Mr. Garrison says the school's been attacked 47 times by eco-terrorists.(see Quotes)
This is another Star Trek reference. The number 47 shows up over and over in ST:TNG, DS9 and Voyager, as it was a script-writer's favourite number.
Eventually many ST writers wrote it into their scripts. Matt and Trey seem to be big Star Trek fans, and this is another homage to ST.