One hour after Yolanda started walking from X to Y, a distance of 24 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? Choose the correct option: A) 24 B) 23 C) 22 D) 21 E) 12
When B started walking Y already has covered 3 miles out of 24, hence the distance at that time between them was   24-3= 
<gadget id="calculator">  24-3</gadget>
<output>21</output>
21 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  21/7= 
<gadget id="calculator"> 21/7</gadget>
<output>3</output>
3 hours. In 6 hours B walked  3*4= 
<gadget id="calculator"> 3*4</gadget>
<output>12</output>
12 miles.   Answer: 12.
<result>E</result>
One hour after Yolanda started walking from X to Y, a distance of 24 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?