求大神解一道微观经济学的题，拜托给点详细解释

Question

Consider the town of Tritown with only three residents, Ed, Jim, and Tony. The three residents are trying to determine how large, in acres, they should build the public park. The table below shows each resident’s willingness to pay for each acre of the park.

Refer to Table 11-1. Suppose the cost to build the park is $30 per acre. How many acres should the park be to maximize total surplus from the park in Tritown?
a.
2 acres
b.
3 acres
c.
4 acres
d.
5 acres

Answer 1

个人认为这道题选择A。
排除来看，C 和D 一共需要成本120和150 显然三个人的WTP 根本就不足以支付建立4和5acres 的park。 再看A和B。 B 三人一共愿意支付96，A为88。消费者的加总剩余就是A最大。所以就选A了。
还有一种方法。根据上面的table，画出他们三人的demand point 并连点得线。单求消费者剩余加总也是等出同样的答案的。