Answer: West Mudville should specialize in, and export, baseball bats.
Step-by-step explanation:
Each country should specialize in the good that it has a lower opportunity cost in producing.
West Mudville
Opportunity cost of producing baseball bats = 9/9 = 1 baseball
Opportunity cost of producing baseball = 9/9 = 1 baseball bat
East Mudville
Opportunity cost of producing baseball bats = 8/4 = 2 baseballs
Opportunity cost of producing baseball = 4/8 = 0.5 baseball bats
From the above, West Mudville has a lower opportunity cost than East Mudville in the production of baseball bats and so it should specialize in and export that.