In an auditorium the ceiling is a horizontal plane 8m above the floor. A speaker stands at one end with the source of sound 1.5m above the floor. A listener is seated 20m away horizontally, at the same height as the speaker's source. Taking the speed of sound as 340ms−1, what is the time interval between the arrival of the direct sound and the sound that reaches the listener after a single reflection from the ceiling?
a) 0.070s
b) 0.019s
c) 0.011s
d) 0.038s