<PRE><B>Question 210725</B>
Well this is a system of 2 equations and 2 unknowns.  Let n = the price of new compact disks and let u = the price of used compact disks.  Then the first equation would be 6n + 2u = 127.92.  The second equation would be 3n+8u = 133.89.&lt;br&gt;

So our system is &lt;br&gt;

6n + 2u = 127.92
3n+8u = 133.89&lt;br&gt;

Since I don&#39;t like working with decimals I would multiply both equations by 100 that way it would get rid of the decimal.  Doing so results in the following system:&lt;br&gt;

600n+200u = 12792
300n+800u = 13389&lt;br&gt;

now we want to know how much one used disk sells for.  to do that we multiply the bottom equation by -2 and add it to the top equation.&lt;br&gt;

-2(300n+800u = 13389) =&gt; -300n-1600u = -26778&lt;br&gt;

Now we add that to the top equation&lt;br&gt;

600n+200u = 12792
+(-300n-1600u = -26778)
----------------------------
-1400u = -13987&lt;br&gt;


now we solve for u by dividing both sides by -1400 and we see that u = 9.99.&lt;br&gt; 

So the price of a used compact disk is $9.99.</PRE>