One hour after Yolanda started walking from X to Y, a distance of 31 miles, Bob started walking along the same road from Y to X. If Yolanda's walking rate was 3 miles per hour and Bobт's was 4 miles per hour, how many miles had Bob walked when they met?	Options
A) 24  B) 23  C) 22  D) 21  E) 16
When B started walking Y already has covered 3 miles out of 31, hence the distance at that time between them was   31-3= 
<gadget id="calculator">  31-3</gadget>
<output>28</output>
28 miles.   Combined rate of B and Y was   3+4= 
<gadget id="calculator">  3+4</gadget>
<output>7</output>
7 miles per hour, hence they would meet each other in  28/7= 
<gadget id="calculator"> 28/7</gadget>
<output>4</output>
4 hours. In 6 hours B walked  4*4= 
<gadget id="calculator"> 4*4</gadget>
<output>16</output>
16 miles.   Answer: 16.
<result>E</result>
One hour after Yolanda started walking from X to Y, a distance of 31 miles, Bob started walking along the same road from Y to X. If Yolanda's walking rate was 3 miles per hour and Bobт's was 4 miles per hour, how many miles had Bob walked when they met?