Question 1014654
<pre>
Line the equations up like this:

{{{system(matrix(2,5, 

15x,""-"",4y,""="",6,
9x,""+"",2y,""="",7))}}} 

To make the y terms cancel, multiply the
bottom equation through by 2, which will 
make the 2y term become 4y which will 
cancel with the -4y term in the top equation,
when we add equals to equals

{{{system(matrix(2,5, 

15x,""-"",4y,""="",6,
18x,""+"",4y,""="",14))}}}

Adding term by term gives:

{{{matrix(1,10,"",33x,"","","","","","",""="",20)}}}

  {{{x}}}{{{""=""}}}{{{20/33}}}

Since that is a nasty fraction, do not substitute it,
as you would if it had been a nice integer. Instead, 
start over and eliminate the other variable:

{{{system(matrix(2,5, 

15x,""-"",4y,""="",6,
9x,""+"",2y,""="",7))}}} 

To make the x terms cancel, the LCM of 15 and 9 is
45.  So we multiply the top equation through by 3,
and the bottom equation through by -5, which will 
make the 15x term become 45x, and the 9x in the
bottom equation become -45x which will cancel when 
we add equals to equals:

{{{system(matrix(2,5, 

45x,""-"",12y,""="",18,
-45x,""-"",10y,""="",-35))}}}

Adding term by term gives:

{{{matrix(1,11,"","","","","","","","",-22y,""="",-17)}}}

            {{{x}}}{{{""=""}}}{{{(-17)/(-22)}}}

            {{{x}}}{{{""=""}}}{{{17/22}}} 



Edwin</pre>