One hour after Yolanda started walking from X to Y, a distance of 10 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? Select
A) 24 B) 23 C) 22 D) 21 E) 4
When B started walking Y already has covered 3 miles out of 10, hence the distance at that time between them was   10-3= 
<gadget id="calculator">  10-3</gadget>
<output>7</output>
7 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  7/7= 
<gadget id="calculator"> 7/7</gadget>
<output>1</output>
1 hours. In 6 hours B walked  1*4= 
<gadget id="calculator"> 1*4</gadget>
<output>4</output>
4 miles.   Answer: 4.
<result>E</result>
One hour after Yolanda started walking from X to Y, a distance of 10 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?