Final answer:
The equation to model the turtle's depth is depth = 11 - 1t.
Step-by-step explanation:
To model the turtle's depth, we can use the equation: depth = starting depth - rate * time.
In this case, the starting depth is 11 feet below the surface. The rate at which the turtle swims downward is 1 foot per second. And the time is represented by the variable 't'.
Therefore, the equation to model the turtle's depth is: depth = 11 - 1t.