I might be able to help a bit here with my physics background. I'm not an electrical engineer, but I know the basics. The complex impedance for an inductor is Z_L = jwL. w (small omega) is 2*pi*frequency. So altogether the equation they are giving is 600 <= 2*pi*100e6*L, which means L >= 9.5e-7, which has units of henries (H).