1. **State the problem:** Marc's family plans to drive a total distance of 150 miles at an average speed of 30 miles per hour. Marc creates the expression $$150 - 30h$$. We need to determine what this expression calculates. 2. **Understand the expression:** The expression $$150 - 30h$$ subtracts the product of speed and time from the total distance. 3. **Recall the formula for distance traveled:** Distance traveled after $$h$$ hours at speed $$30$$ mph is $$30h$$ miles. 4. **Interpret the expression:** Since $$150$$ is the total distance and $$30h$$ is the distance traveled after $$h$$ hours, the expression $$150 - 30h$$ represents the remaining distance to be traveled after $$h$$ hours. 5. **Conclusion:** Marc's expression calculates the distance remaining after $$h$$ hours of driving. **Final answer:** The distance remaining after $$h$$ hours of driving.