A 20.0-m-long cable consists of a solid-inner, cylindrical, nickel core 10.0 cm in diameter surrounded by a

Question:

A 20.0-m-long cable consists of a solid-inner, cylindrical, nickel core 10.0 cm in diameter surrounded by a solid-outer cylindrical shell of copper 10.0 cm in inside diameter and 20.0 cm in outside diameter. The resistivity of nickel is 7.8 X 10-8 Ωm.
(a) What is the resistance of this cable?
(b) If we think of this cable as a single material, what is its equivalent resistivity?