Question 1173247
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            When I see a system of equations like this one,  I have ready and I use my standard mantra.   It says:



<pre>
The two given equations have identical left sides - - - hence, their right sides are equal

    3x + 7 = -4x + 21.


From this equation

    3x + 4x = 21 - 7

      7x    =    14

       x    =    14/7 = 2.


Then y = 3x + 7 = 3*2 + 7 = 6 + 7 = 13.


<U>ANSWER</U>.  x= 2,  y= 13.
</pre>

Solved.


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My mantra is short and makes the solution short - - - THEREFORE, &nbsp;I like it &nbsp;(!)


You may use it, &nbsp;too &nbsp;(!)