How far from a cliff should a boy stand in order to hear the echo of his clap 0.9s later? (Speed of sound in air = 330 ms-1)

How far from a cliff should a boy stand in order to hear the echo of his clap 0.9s later? (Speed of sound in air = 330 ms^-1)

The correct answer is C. 148.50m

v = 2x/t â´ distance x = vt/2 = 148.5m