λν=c where λ is the wavelength, ν is the frequency and c is the speed of light;
if λ = 1.2km = 1.2×10^3 m, then:
λν=c, and ν = c/λ
[tex]v = (3.0 \times {10}^{8})m/s \div (1.2 \times {10}^{3})m \\ v = 2.5 \times {10}^{5} \: \: 1/s = {s}^{ - 1} = hz[/tex]
