3 x 10^-2 / 12 x 10^4
I expect that you mean
(3 x 10^-2) / (12 x 10^4)
$$\\3/12 * 10^{-2-4}\\ =0.25*10^{-6}\\ =2.5*10^{-1}*10^{-6}\\ =2.5*10^{-7}$$