John started driving on a highway at a constant speed of R miles per hour at 13:00. Then, 2 hours later, Tom started driving on the same highway at a constant speed of 5R/3 miles per hour at 15:00. If both drivers maintained their speed, how many miles had John driven on the highway when Tom caught up with John?  Choose one:
A) 3R
B) 5R
C) 8R
D) 9R
E) 10R
In 2 hours, John drove 2R miles.   Tom can catch John at a rate of 5R/3 - R = 2R/3 miles per hour.   The time it takes Tom to catch John is 2R / (2R/3) = 3 hours.   In 3 hours, John can drive another 3R miles for a total of 5R miles.   The answer is 5R.2  / (2 /3)= 
<gadget id="calculator">2  / (2 /3)</gadget>
<output>3</output>
3 hours.   In 3 hours, John can drive another 3R miles for a total of 5R miles.   The answer is 5R.
<result>B</result>
John started driving on a highway at a constant speed of R miles per hour at 13:00. Then, 2 hours later, Tom started driving on the same highway at a constant speed of 5R/3 miles per hour at 15:00. If both drivers maintained their speed, how many miles had John driven on the highway when Tom caught up with John?