A boy is standing on a straight road with two high buildings behind him on the same line. Building A is 80m behind him, and Building B is 120m further behind Building A. He fires a starting pistol. Take the speed of sound in air to be 340m/s.
(i) Find the time after firing when he hears the first echo.
(ii) Find the time gap between the first and the second echoes that reach him.