A deep-sea autonomous underwater vehicle (AUV) is deployed to study the seabed. It descends vertically from the ocean surface.
The graph below shows the depth, in metres, reached by the AUV during the first 12 minutes12\text{ minutes}12 minutes of its descent.
Determine the constant speed of the AUV between 8 minutes8\text{ minutes}8 minutes and 12 minutes12\text{ minutes}12 minutes of its descent, in m min−1\text{m min}^{-1}m min−1.