A student claps his hands in front of a wall and hears the echoes. He claps at the same moment as he hears the echo of the previous clap. Another student starts a stop-watch on the first clap and stops it on the eleventh clap. The reading on the stop-watch is 9.4 s and the speed of sound is 320 m/s. The diagram shows the student at distance x from the wall. (NOT TO SCALE) What is the distance x between the student and the wall?

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.