Tina lives 30 miles away from her work, and she normally drives at 45 miles per hour. If she wants to get to work 15 minutes earlier, how fast should she drive to work, in miles per hour?
Distance / rate = time
Her ususal time is thus 30 m / 45 m/hr = 2/3 hr or 40 minutes
take away 15 minutes results in 25 minute travel time
distance /rate = time time will be 25 /60 of an hour
30 / rate = 25/60 hr
30 * 60/25 = rate = 72 m/hr