The Capacitance Per Unit Length of a Very Long Coaxial

Multiple Choice

The capacitance per unit length of a very long coaxial cable,made of two concentric cylinders,is
50 pF/m.What is the radius of the outer cylinder if the radius of the inner one is 1.0 mm?
(k = 1/4πε₀ = 8.99 × 10⁹ N • m²/C²)

A) 3.0 mm
B) 2.0 mm
C) 4.0 mm
D) 1.0 mm
E) 0.50 mm