I'm not able to solve this problem, but thought maybe some genius out there would do better

The p in front of the materials Ω pr meter should be a ρ, but I hope that you understood that. I have come to the expression R=ρ*(dx/(phi*r^2)) using the hint, since the formula for resistance in a cable is, R=ρ*(length/cross section). And here dx would represent the length, and phi*r^2 the cross section if you are using the hint.

But I'm not even sure that is correct. I guess that calling the "length" dx has to to with the integration, but would not dr make more sence, since r has to be the variable here? Or maybe I'm far out now. So if there are any math-genius with some time to spare out there I would really appreciate some help