
You are definitely not the first person to make a careless mistake PB, we all do it!!! 
But 200 kilometers by 100 kilometers is still pretty humongous...that is about 124 miles by 62 miles.
I can still answer the question anyway, though.
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perimeter = length + length + width + width
perimeter = 200 + 200 + 100 + 100
perimeter = 600 kilometers
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area = length × width
area = 200 × 100
area = 20,000 square kilometers
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You can just replace the word "kilometers" with whatever units you have. 