Question 1098064
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<pre>
The second courier started when the distance between them was 2*7.5 = 15 miles.


The distance between them decreases at the rate of 1 mile per hour. (8.5-7.5 = 1).


Having this, everybody can conclude that the answer is 15 hours.
</pre>


For this type of problems, "catching up" problems, see the lessons

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=http://www.algebra.com/algebra/homework/word/travel/Travel-and-Distance-problems.lesson>Travel and Distance problems</A>  

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=https://www.algebra.com/algebra/homework/word/travel/Typical-catching-up-Travel-and-Distance-problems.lesson>Travel and Distance problems for two bodies moving in the same direction (catching up)</A>

in this site.