A maintenance robot is inside an empty storage tank. Its ultrasound sensor is 6.8 m from wall P and 15.3 m from wall Q. The sensor sends a separate pulse directly towards each wall and detects the returning echo. The speed of ultrasound in the air is 340 m/s.
What is the difference between the return times of the two echoes?
0.025 s0.025\ \mathrm{s}0.025 s
0.090 s0.090\ \mathrm{s}0.090 s
0.130 s0.130\ \mathrm{s}0.130 s
0.050 s0.050\ \mathrm{s}0.050 s