Δ f = \frac{c}{2 d} = \frac{3 \cdot 10^{8}}{2 \times 0, 15} = 10^{9} H z

${\Delta f =\frac{c}{2d}=\frac{3 \cdot 10^8}{2 \times 0,15}= 10^9\, \mathrm{Hz}}$

Error