For the purely competitive firm: i. the supply curve is the marginal cost curve above the shutdown point. ii. the shutdown price is lower than $15. iii. the supply curve is the average variable cost curve above $15. iv. the supply curve is the average total cost curve above $10. v. the shut down price is just below $10.

It is pi over 6:

We first solve this by determining how many times it goes around the circle. When you turn 25pi/6 into a mixed number you get 4pi + 1pi/6. Since it takes 2pi to get around the circle once, you go around the circle twice with 4pi. This leaves with 1pi/6 left at the starting point. The answer is pi/6. 13pi/6 also has the same terminal angle but it is not in range of answers (they are asking for 0-2pi)