The region of integration is the triangle with the vertices (0, 0), (8, 0) and (8, 4). It is formed by y=0, x=8 and y=x/2, or x=2y. When outer integral is by y, y changes from 0 to 8/2=4. And for any given y x changes from 2y to 8.

So the correct answer is 2.

Please ask if something is unclear.

Oct 21st, 2015

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