.Evaluate the given integral by changing to polar coordinates.

whereDis the region in the first quadrant that lies between the circlesx^2 +y^2 = 16 andx^2 +y^2 = 4x.

I'm confused on how to find the boundaries, since the second equation doesn't equal a constant. I changed everything to polar coordinates and got r^2 cos ^2 x+r^2 sin ^2 x=16 so, r^2 = 16, r =4 so one of the boundaries would be 0 to 4. Also, when I change the integral to polar coordinates, I got the double integral of rcosx r dr dtheta. How do I find the other boundaries?

Thanks so much!