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 3 rd red light and the 21st red light?
Note: 1 foot is equal to 12 inches.
Answer Choices
A. 18
B. 18.5
C. 20
D. 20.5
E. 22.5