Fred can construct 1 shed in 40 hours and 1 shelf in 10 hours.
So,
Opportunity cost of 1 shelf = 10/40 = 0.25 sheds
Sandy can construct 1 shed in 32 hours and 1 shelf in 4 hours.
So,
Opportunity cost of 1 shelf = 4/32 = 0.125 sheds
Sandy can produce shelf at lower opportunity cost.
So,
Sandy will specialize in production of shelf and would trade with Fred.
Since, opportunity cost of 1 shelf for Fred is 0.25 Shed, the maximum price that he would be willing to pay for shelf is 0.25 sheds.
Hence, the correct answer is the option (d) [0.25 sheds].