During a cave survey, a sound transmitter and detector are placed together. A pulse reflected from a rock column returns to the detector after 0.030 s. The back wall of the cave is 5.1 m farther from the detector than the rock column. Sound travels at 340 m/s. How long after the pulse is transmitted does the echo from the back wall return?
0.045 s0.045\ \mathrm{s}0.045 s
0.015 s0.015\ \mathrm{s}0.015 s
0.090 s0.090\ \mathrm{s}0.090 s
0.060 s0.060\ \mathrm{s}0.060 s