I have a homework question that i simply can't get my head around, and it's driving me nuts, any help would be greatly appreciated,

The question wants me to calculate the moment of inertia for a thin disk radius b with uniform density p, that lies in the x-y plane.

But it wants me to find the moment of inertia about the x axis, using polar co ordinates.

I have worked this out using perp. axis thm but i'm not allowed to use that here, have to calculate from scratch.

thanks for any help.