An autonomous underwater vehicle (AUV) maps the seabed using active sonar.
Figure 1 shows the AUV transmitting an ultrasound pulse down to a flat section of the ocean floor.

The sound waves reflect off the seabed and are received back at the AUV's sonar transducer.
The speed of sound in seawater is 1520 m/s.
The time between the transmission of the pulse and its detection is 85 milliseconds.
Calculate the distance, ddd, from the AUV to the seabed.