Halliday, Resnick & Walker — Motion Along a Straight Line: Problem 95

Speed limits. (a) The greatest speed limit in the United States is along the tolled section of Texas State Highway 130 where the limit is 85 mi/h. How much time would be saved in driving that 41 mi section at the speed limit instead of 60 mi/h? (b) The speed limit in residential areas is commonly 25 mi/h but some motorists drive at an average speed of 45 mi/h, perhaps by weaving through traffic and even driving through traffic lights that had just turned red. How much time would be saved in driving at that faster speed through 5.5 mi instead of the posted speed limit if the car does not stop at any intersections?