A nonconducting spherical shell problem

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To achieve a uniform electric field within a nonconducting spherical shell with a positive charge density p = A/r, the value of A must be determined. The problem involves a spherical shell with inner radius a = 2.00 cm and outer radius b = 2.40 cm, containing a central charge q = 45.0 fC. The user is unsure how to approach the solution and which equations to apply, particularly questioning the appropriate value of r for calculations. It is clarified that r is a variable that can take any value between the inner and outer radii of the shell. Understanding the relationship between the charge density and the electric field is crucial for solving the problem.
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A nonconducting spherical shell of inner radius a=2.00 cm and outer radius b = 2.40 cm has (withing its thickness) a positive charge density p = A/r, where A is a constant and r is the distance from the center of the shell. In addition, a small ball of charge q=45.0 fC is located at that center. What value should A have if the electric field in the shell (a\leqr\leqb) is to be uniform?

I know the answer that A value is 1.79\times10-11. The problem is I don't know how to solve it. I don't even know which equation I should use. I tried to start with E = kq/r2, but what is the value of r. It is not specified where should I calculate.

Please help.
Thank you.
 
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r can have any value between a and b. It is a variable, with no specific value.

Do you know what charge the "q" refers to in your equation for E?
 

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