Didn't get any of that so had to redo in metric.

speed of light = 3 x 10^8 m/s

3 GHZ = 3 x 10^9 /s

So 3 x 10^8 / 3 x 10^9 = 0.1 metre = 10 centimetre = okay, 3.9 inches

But then metric always saves your ass. Back in physics class, they'd ask you how deep the well was if you dropped a stone & heard the water splash in 10 seconds. Before the American students could even begin their work, all the Indians would yell "500 metres!" And that's cause the gravitation constant is 10, so one half 10 times 10 times 10 is 500.