一个汽车公司打算停止销售X型车，转售SX型车（一种基于X的改装车型）。X型车年销售额为3,000,000元，但成本是1,500,000元。 SX型车年销售额预计可达4,000,000元，但是每年另需300,000元的设计费和升级安装费1,100,000元（也需加上1,500,000元的成本）。问：机会成本是多少？

原题：Super Cars Ltd. is considering discontinuing model X in order to produce model SX, a sportier version. Model X annual revenue is $3,000,000 with expenses of $1,500,000. Model SX is expected to make $4,000,000 of revenue each year however there will be extra design fees of $300,000 and mechanical upgrades of $1,100,000 every year. What is the annual opportunity cost?

过程是：x的净利润=3000000-1500000=1500000

sx的净利润=4000000-1500000-1100000-300000=1100000

答案是$400,000，我有点困惑，所以讲解，谢谢！