给定某种商品的需求曲线是D=14-P。
1. 这种商品只由垄断企业A提供供给。企业A的总成本曲线是C=2Q+1，求这个企业最合适的供给量和价格；
2.由于市场的需求扩大，需求函数变为D=2(14-P)。除了上述的企业A之外，与A拥有同样总成本曲线的B企业也加入市场竞争（假定市场只有A，B2个企业）。求在纳什均衡的情况下，各企业的产量和价格；
3.由于市场继续扩大，市场变为完全竞争市场。所有新进入企业的总成本曲线均为C=2Q+1，此时均衡价格将为多少？并说明理由。

题目是自己翻译的，可能翻译的不太好～这里附上原版的题目。求高手解答，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.