1. Peppy Pets charges a flat fee of $15 plus $3 per hour to keep a dog during the day. Happy Hounds charges a flat fee of $21 plus $1 per hour. For how many hours is the total fee charged by the companies the same?

x represents the amount of hours
peppy pets 15 + 3x
happy hounds 21 + x

15 + 3x = 21 + x
subtract x from both sides

15 + 2x = 21
subtract 15 from both sides

2x = 6
divide each side by 2

x = 3 hours