Here is an interesting post explaining how to calculate the speed of light. Some of the formulas are AP physics level, but the concepts are understandable even if you don’t know exactly how the formulas work.
If you plug in the actual numerical values for the vacuum permittivity and permeability, it works out to 299,792,400 meters per second—precisely the speed of light!
So what does this mean? … [I]t gives us a clue as to why the speed of light in vacuum is what it is; it’s the speed where electric and magnetic forces balance out to create a stable electromagnetic wave packet that can travel indefinitely. Any slower and the photon would come undone, just as the wires would be pushed apart by the electric repulsion. Any faster, and the magnetism would overcome that repulsion and draw them together, collapsing the system. With nothing more than high school-level math, it’s easy to show that the speed of light in a medium (or in the vacuum of space) inevitably arises as a consequence of that medium’s electric permittivity and magnetic permeability.