Another Calc III problem

Here is one more problem I mailed to a guy which I couldn't solve there in Neckers. It was easy. I had to convert a double integral from cartesian to Polar coordinates and I kept doing the same mistake. Its only when I came back home and revised the relevant material and worked out more problems then I realized my mistake. Now I am glad that he will be able to use it before his class at 11 am today. I typed it in Maple 10, which now has a much better documentation feature, almost like Mathematica, perhaps better.