Final answer:
The distance between the submarine and the aircraft is 1800 m.
Step-by-step explanation:
To calculate the distance between the submarine and the aircraft, we can use the speed of sound in water and the time it takes for a sonar echo to return. Let's assume the speed of sound in water is 1500 m/s. Given that the echo returns to the submarine 1.20 s after being emitted, we can use the formula distance = speed * time to calculate the distance. Therefore, the distance is 1800 m.