well, in short, the students and chaperones are at a 2 : 9 ratio, and we know there are 171 students, how many chaperones then, so long they maintain a 2:9 ratio?

Cos 210° = cos ( 180° + 30° ) - cos 30° = - √3/2
You have to convert 50 feet to inches, so you take 50 times 12 and get 600. Then, you take 600/75 to get the number of rotations. Your final answer shold be 8 rotations.
Is 10 and 15 because they both have a value of .909