Radio waves are electromagnetic waves. The speed of the electromagnetic waves is the speed of light, a constant. In the space (vaccum) the speed of light is approximately 300,000 km/s.
Now you can calculate the time to travel 8.00 * 10^7 km
V = d / t ==> t = d / v = 8 *10^7 km / 3*10^5 km/s = 2.66 * 10^2 s = 266 s.
You do not need to use the frequency.
