You are standing 100 meters from a concrete wall and your friend Billy is 200 meters farther away, on the same side of the wall. When you make a loud, barbaric yelling sound, Billy hears both the original sound and the echo. If the speed of sound in air is taken to be 300 meters per second, what is the difference in time, in seconds as a decimal rounded to the hundredths place, between when Billy hears the original yell versus the echoed yell off of the concrete building?