I need help with part(a)and(b)of this question:

My attempt:

(a)So here's my sketch of the region:

So why is it that we can't evaluate the double integral as an iterated integral? Is it because the region is not one rectangle, but made up of several rectangles? I don't know how to answer this...

(b)What kind of geometric series do I need to use here? What do I need to do here?