求解一道英语经济学题目～

马上要研究生考试了，这是过去的考题，自己做出来不确定是否正确，求高手解答一下！谢谢！
Assume that the demand for a good in the market is D = 14 - p, where p is its
price. Then, answer the following questions. Show all your work.
(1) Suppose that firm A is a monopolist. Its cost function CA for the amount
QA of production is CA = 2QA + 1. Then, what is the optimal amount for
this firm to produce and the price in the market?
(2) Suppose the market expands such that the demand function is D = 2(14-p).
Then, in addition to the above firm A, a new firm B whose cost function
is identical to firm A’s enters this market. When the firms compete in
quantities of a production in this market, what are the optimal amounts of
production for each firm, and the price in the Cournot–Nash equilibrium?
(3) Suppose the market contains to expand and entry of new firms continues. No
firm has any influence over the price, and therefore this market is perfectly
competitive. The cost function for each firm i entering this market is Ci =
2Qi+1. Then, what is the price in this market? Explain why the price goes
to this level.

im not sure if i did it right, especially the third one....
:)