1. 2πrB = μI from Ampère's circuital law where r is the separation between wires.

2. εμ = 1/c2 from the EM wave equation where c = speed of light ≈ 3 x10?.

The Ampère which is defined as the amount of current that generates a force of 2 dynes per centimeter of length between two wires one centimeter apart.

Combine the first two equations to get μ = 4 π x 10??.

Combine that with the third equation to get ε = 1/(μc2) ≈ 10??/(9 x 4π).

Reference:?

Where does 1/4(pi) in vacuum permittivity come from??

Roy McCammon

https://www.quora.com/Where-does-1-4-pi-in-vacuum-permittivity-come-from

https://e-magnetica.pl/magnetic_permeability_of_vacuum