Solving a problem in physics section 1 paragraph 12 ele

12. The electrostatic field is generated by an infinitely long cylinder of radius R = 7 mm, uniformly charged with a linear density of ? = 15 nC / m. Define: 1) E field intensity at points of the cylinder axis at a distance r1 = 5 mm, r2 = 1 cm; 2) the potential difference between two points of the field lying at a distance r3 = 1 cm and r4 = 2 cm from the surface of the cylinder, in its middle part.