How Is Charge Density Calculated in Coaxial Cables?

[v_pino]

Homework Statement

I have attached the question as a pdf.

Homework Equations

I'm thinking that we take the line integral of voltage to get electric field. But I'm not sure how to proceed from here. Is the line integral from a to b? Also, how do I get the charge density having found the electric field?

Also, do I need to consider the dielectric in this part of the question?

The Attempt at a Solution

 

[rude man]

Can you compute the capacitance per unit length between the inner & outer conductors?