平狄克微观经济学11章Pricing with market power课后题的疑惑，求解答，谢谢

13.  Some years ago, an article appeared in the New York Times about IBM’s pricing policy. The previous day, IBM had announced major price cuts on most of its small and mediumsized computers.  The article said:  IBM probably has no choice but to cut prices periodically to get its customers to purchase more and lease less.  If they succeed, this could make life more difficult for IBM’s major competitors.  Outright purchases of computers are needed for ever larger IBM revenues and profits, says Morgan Stanley’s Ulric Weil in his new book, Information Systems in the ‘80’s.  Mr. Weil declares that IBM cannot revert to an emphasis on leasing.
What factors determine whether leasing or selling is preferable for a company like IBM?  Explain briefly.

答案： There are at least three factors that could determine whether leasing or selling is preferable for IBM.  The first factor is the amount of consumer surplus that IBM could extract if the computers were leased and a two-part tariff scheme were applied.  The second factor is the relative discount rates on cash flows: if IBM has a higher discount rate than its customers, it might prefer to sell; if IBM has a lower discount rate than its customers, it might prefer to lease.  A third factor is the vulnerability of IBM’s competitors.  Selling computers would force customers to make more of a financial commitment to one company over the rest, while with a leasing arrangement the customers have more flexibility.  Thus, if IBM feels it has the requisite market power, it might prefer to sell computers instead of lease them.

请问第二点的discount rates贴现率怎么解释呢？（本人大一水平，未学宏观）
而且为什么就是这个逻辑呢？
第三点可以解释为 顾客对IBM公司的忠诚度吗？或者说，是market power的大小？

还有第二题：

If the demand for drive-in movies is more elastic for couples than for single individuals, it will be optimal for theaters to charge one admission fee for the driver of the car and an extra fee for passengers.  True or false?  Explain.
答案： True.  This is a two-part tariff problem where the entry fee is a charge for the car plus driver and the usage fee is a charge for each additional passenger other than the driver.  Assume that the marginal cost of showing the movie is zero, i.e., all costs are fixed and do not vary with the number of cars.  The theater should set its entry fee to capture the consumer surplus of the driver, a single viewer, and should charge a positive price for each passenger.

答案好像没说为什么two part tariff比单一价格要好啊？
而且因为elasticity很大，为什么选择two part tariff不能看成是把价提高了？这样quantity demanded会减少？
如果只是选择单一价格，可以允许有些在有two part tariff情况下不买的顾客购买。
请问我的理解的错误在哪儿呢？谢谢！

为什么two part tariff比单一价格要好？
因为two part tariff可以实现效率标准：P=MC，而单一价格是按照MR=MC来确定的，会造成无谓损失。