请问我第二问做的对吗？不对的话，正确的做法是什么呢？
An owner of a small firm needs to hire some managers. Assume that each manager has time to do only one task. Task A is worth $100,000 to the owner. Task B is worth $75,000 and Task C is worth $50,000. The owner hires only two managers, having one do Task A and the other do Task B. What is the opportunity cost of Task B?
In the above problem, assume the firm still has only two managers. Assume further that each manager can do the other’s task with the same efficiency. What is the value of the second manager (i.e. what would the firm lose if it fired [and did not replace] the second manager)? What is the value of the first manager (when the second is still employed)?
a. The opportunity cost of Task B=$100,000/$75,000=4/3 task A

b. Assume the efficiency of the first manager on doing task A is X, and the efficiency of the second manager on doing task B is Y.
The value of the second manager=(X+Y)/Y
The
value of the first manager (when the second is still employed)=Y/X