We're down 125*5 (for 5 days), so we subtract that to start it off. Next, he gets 12 dollars per every wind chime, and we can write every wind chime sold as x to get -625+12x. Next, we need that to equal 3500, so we get -625+12x=3500. Adding 650 to both sides, we get 4125=12x. After that, we divide both sides by 12 to get 4125/12=x