Question 1173765
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<pre>

Use this proportion


    {{{140000/100}}} = {{{21000/x}}},


where x is the unknown value under the problem's question.


This proportion says that the miles per dollar are the same in both cases.


From the proportion, find


    x = {{{(100*21000)/140000}}} = 15  dollars.    <U>ANSWER</U>
</pre>

Solved.


Very simple and elegant solution (!)