This of a clock and label it
Every 1/2 hour (30 minutes) would be the neck so at the numbers 6 and number 12.
Every 1/3 hour (20 minutes) would be the leg so at the numbers 4,8, and 12.
Everyone 1/6 hour (10 minutes) would be the arm so at numbers 2,4,6,8,10 and 12.
If I understand the question it os asking what body part is being stretched at 2/3 hour which is at the second 20 minute interval, the number 8. Both the leg and arm fall on the number 8.