A man standing at the front of a cliff hears an echo of a gunshot after 3 seconds. After moving closer by 82.5 m, he fires again and hears the echo in 2.5 seconds. The distance of the cliff from the initial position and the speed of sound is:
a) 247.5 m, 165 m/s
b) 165 m, 247.5 m/s
c) 247.5 m, 332 m/s
d) 332 m, 247.5 m/s
