如果在一个地方建一所医院可以为当地人民带来价值50万元的利益,而建一所学校会为当地人民带来价值60万的利益。而医院的成本是20万,学校的成本是40万。请问建一所学校所导致的真实经济花费是多少?In an area, building a hospital can bring $500,000 valued benefits to local people, and building a school can bring $600,000 valued benefits to local people. The cost of building a hospital is $200,000, while that of building a school is $400,000. What is the economic cost of building a school?
10万 $100,000
20万 $200,000
30万 $300,000
60万 $600,000