A rope is swinging in such a way that the length of the arc is decreasing geometrically. If the first arc is 18 feet long and the third arc is 8 feet long, what is the length of the second arc?
1. 12 feet
2. 10 feet
3. 5 feet
4. 72 feet
1. 12 feet
2. 10 feet
3. 5 feet
4. 72 feet