Scenario 8-2 Lincoln Offers to Do Katelyn's Housework for $80 Per Week.Katelyn's

Scenario 8-2
Lincoln offers to do Katelyn's housework for $80 per week.Katelyn's opportunity cost of doing housework is $100 per week, and Lincoln's opportunity cost of doing housework is $60 per week.
-Refer to Scenario 8-2.What will be Lincoln's gain in producer surplus as a result of the proposed transaction

A) Lincoln will gain $20 per week.
B) Lincoln will gain $30 per week.
C) Lincoln will gain $40 per week.
D) Lincoln will gain $50 per week.