Small lights are hung on a string 6 inches apart in the order red, red, green, green, green, red, red, green, green, green, and so on continuing this pattern of 2 red lights followed by 3 green lights. How many feet separate the 3rd red light and the 21st red light?
Note: 1 foot is equal to 12 inches.
This problem is copyrighted by the American Mathematics Competitions.
Instructions for entering answers:
For questions or comments, please email firstname.lastname@example.org.