.
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.
Solved.