If it takes two hours to travel 30 miles by bike, it means that the average speed / (the average rate)  is  

     = 15 miles per hour.


If the rate remains the same, then the time to travel 105 miles is

     = 7 hours.    ANSWER



Or, alternatively, you may write a proportion

     =     (which is  in both scenarios)

and find x from there.  You will get the same answer.


Notice that the proportion expresses the fact that the average rate remains the same.