If all the planets were in a row then if would only take 4 minutes because in this position, however this postion is just as common as when the Earth and Mars are on opposite sides of the Sun. In this position it takes 24 minutes for information to travel because Earth and Mars are 24 light minutes. So on average the Earth and Mars are 14 light minutes away so on average a message from Mars would take from 4 to 24 minutes to reach Earth.