Question

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Answer 1

As seen in the chart  B has the comparative advantage in coal because 1/3 > 1/5 It means they are better at producing coal than the U.S.Have in mind examples like:
U.S. 
1 barrel of oil = 4 hrs 
1 ton of coal = 5 hrs 

B 
1 barrel of oil = 7 hrs 
1 ton of coal = 3 hrs 
After seeing this we can say that the country which has more availability has a comparative advantage over other countries.
Hope this helps

Answer 2

Country B has the comparative advantage in coal because in 1 hour they can produce 1/3 ton of coal which is more than the US who produces 1/5 ton of coal in the same amount of time. I think that the country which has more availability will end up having the comparative advantage over the other countries. International trade is based on the comparative advantage and most developing Arabic countries have the availability of oil have the comparative advantage.