The situation describes the remaining percentage of a workout over a period of 30 minutes. The domain of this scenario refers to the possible values for time that are relevant to the workout, which is from the start (0 minutes) to the end (30 minutes).
Given these considerations, the correct answer that describes the domain of this situation is:
a. all real numbers greater than or equal to 0 and less than or equal to 30.
This choice accounts for every possible minute within the 30 minutes of the workout.