Mark can produce 60 baseballs in a month and Katie can produce 42 baseballs in a month. Also, Mark can produce 40 bats in a month and Katie can produce 30 bats in a month. has the absolute advantage in the production of bats, and has the comparative advantage in the production of bats.

The answer is "Mark and Katie".

Explanation:

Through one month, Marked could manufacture 60 baseballs, but also Katie could manufacturing process 42 baseballs a couple of weeks, and inside the same month Katie may generate 40 bats in the same month 30 bats. In bats, Mark now has comparative advantages and Katie will have the peak value in bats production.