To represent the submarine's position relative to the surface after 6 minutes, we can set up the following expression:
Let \( d \) be the depth of the submarine below the water's surface in meters. Since the submarine descends at a rate of 50 meters per minute, after \( t \) minutes, the depth can be expressed as:
\[ d = 50t \]
After 6 minutes, we can substitute \( t \) with 6:
\[ d = 50 \times 6 \]
Calculating this gives:
\[ d = 300 \]
Thus, the submarine's position relative to the surface after 6 minutes is:
\[ d = 300 \text{ meters} \]
So the expression representing the submarine's position after 6 minutes is \( d = 50 \times 6 \), and the numerical value is 300 meters below the water surface.