How long would it take a radio wave to travel between Earth and Mars (8.00*10^7km)

(8.00*10^7km) = 8.00 X 10^10 meters

traveling at the speed of light , 3.00 X 10^8 meters / sec


(8.00 X 10^10 meters) / (3.00 X 10^8 meters / sec) = 267 seconds

267 seconds
aka
4 minutes & 27 seconds