Answer
b. Ron is washing, David in mowing.
Work Step by Step
Since David can mow a lawn and only give up washing 2 cars, David has an absolute advantage in mowing since Ron would have to give up washing 3 cars. Since Ron can wash 3 cars and only give up mowing a lawn, Ron has an absolute advantage in washing since David could only wash 2 cars with giving up mowing a lawn.
