A long, solid, non-conducting cylinder of radius 10 cm has a non-uniform volume density, ρ, that is a function of the radial distance r from the axis of the cylinder. ρ = A*r2 where A is a constant of value 2.1 μC/m5.

A) What is the magnitude of the electric field 9 cm from the axis of the cylinder?

B) What is the magnitude of the electric field 11 cm from the axis of the cylinder?

Please include detailed work.
Here is how i tried to do it, tell me where i went wrong.

Since P has a nonuniform volume density, i have to derivate q/v so P=dq/dv.
So, dq=dv*P
Integrating i get q=Integral(P*dv)

Question

A long, solid, non-conducting cylinder of radius 10 cm has a non-uniform volume density, ρ, that is a function of the radial distance r from the axis of the cylinder. ρ = A*r2 where A is a constant of value 2.1 μC/m5.

A) What is the magnitude of the electric field 9 cm from the axis of the cylinder?

B) What is the magnitude of the electric field 11 cm from the axis of the cylinder?

Please include detailed work. 
Here is how i tried to do it, tell me where i went wrong.

Since P has a nonuniform volume density, i have to derivate q/v so P=dq/dv.
So, dq=dv*P
Integrating i get q=Integral(P*dv)