Flux Calculation for Disk Geometry

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Homework Statement

http://img13.imageshack.us/img13/88/fluxm.th.jpg

Homework Equations

The Attempt at a Solution

I am having difficulties to work this problem out. I know the formula is :

http://img13.imageshack.us/img13/4883/formmix.th.jpg

 

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I think my problem is to represent the 7r into x y z, is it 7x + 7y + 7k