## Improper double integral

Hi, my question is:

Consider the improper double integral of 1/(x^2+y^2)^2 dy dx, limits for y: 0 to infinity, limits for x: 1 to infinity
Make the substitution z=y/x in the inner integral, for each fixed y>=1, and hence determine whether the double integral converges.

I'm really stuck on this question, so any help would be greatly appreciated