Answer: Bess had been keeping track of the storm for 14 hours.
Explanation:
Since we have given that
Number of miles he recorded yesterday = 135 miles
Number of miles he recorded today = 75 miles
Total number of miles = 135+75=210 miles
Speed = 15 miles per hour
So, Time taken is given by

Hence, Bess had been keeping track of the storm for 14 hours.