With complicated numbers like this, we usually just read exactly what it says. So instead of reading "1/8" as "one eighth," we would describe it exactly as written.
A. 1/299792458 = one over two hundred ninety-nine million seven hundred ninety-two thousand four hundred fifty-eight
B. 6.62607015×10^−34 = Six point six two six zero seven zero one five times ten to the negative thirty-fourth power
The others would be read aloud like B above.
One distinction: If it's written as a fraction, we would say "over" for the "/" symbol. The "÷" symbol would be read as "divided by."