Alice and Bob play a game involving a circle whose circumference is divided by 18 equally-spaced points. The points are numbered clockwise, from 1 to 18. Both start on point 18. Alice moves clockwise and Bob, counterclockwise. In a turn of the game, Alice moves 7 points clockwise and Bob moves 8 points counterclockwise. The game ends when they stop on the same point. How many turns will this take?
6
8
9
12
18
