Mr. Goldstein is driving to Houston. The equation y = -45x + 270 represents the numbers of miles that he still has to travel after driving for x hours. What is the slope of the line and what does it represent in this situation?

-45 and it represents the number of miles he had to drive

-45 and it represents the number of driving miles per hour

270 and it represents the driving miles per hour

270 and it represents how many miles he had to drive