Question 965300
<pre>
{{{system(expr(1/4)x-6y=-70,
      5x+expr(3/4)y=49)}}}

Before using elimination, get rid of the fractions by 
multiplying them through by the least common denominator of 4:

{{{system((red(4))*expr(1/4)x-(red(4))*6y=(red(4))*-70,
      (red(4))*5x+(red(4))*expr(3/4)y=(red(4))*49)}}}{{{"<--->"}}}{{{system((cross(red(4)))*expr(1/cross(4))x-(red(4))*6y=(red(4))*-70,
      (red(4))*5x+(red(cross(4)))*expr(3/cross(4))y=(red(cross(4)))*49)}}}

{{{system(matrix(2,5,  x,""-"",24y,""="",-280,

20x,""+"",3y,""="",196))}}}

We notice that the y terms will cancel if we multiply the second 
equation through by 8 to make the +3y become +24y. then it will
cancel with the -24y term in the first equation:

{{{system(matrix(2,5,  x,""-"",24y,""="",-280,

160x,""+"",24y,""="",1568))}}}
------------------------------
{{{system(matrix(1,11,"",161x,"","","","","","",""="","",1288))}}}
      {{{x}}}{{{""=""}}}{{{1288/161}}}
      {{{x}}}{{{""=""}}}{{{8}}} 

Finish by subtituting 8 for x in any of the above equations
which contain both letters.  I'll pick this one

{{{matrix(1,5,20x,""+"",3y,""="",196))}}}
{{{matrix(1,5,20(8),""+"",3y,""="",196))}}}
{{{matrix(1,5,160,""+"",3y,""="",196))}}}
{{{matrix(1,5,"","",3y,""="",36))}}}
{{{matrix(1,5,"","",y,""="",12))}}}

The solution is (x,y) = (8,12)

--------------------------------------

b.) {{{system(expr(1/4)x+expr(33/2)=y,
      y-12=-2x)}}}

Multiply the first one through by 4

{{{system(red(4)*expr(1/4)x+red(4)*expr(33/2)=red(4)*y,
      y-12=-2x)}}}

{{{system(x+66=4y,y-12=-2x)}}}

Now we need to line the terms up su that the x terms come first,
the y-terms come second, the equal signs come third and the constant
terms come fourth.  We do that by adding and subtracting terms from
both sides until they get like this:

{{{system(matrix(2,5,  x,""-"",4y,""="",-66,

2x,""+"",y,""="",12))}}}

We notice that the x terms will cancel if we multiply the first 
equation through by -2 to make the x become -2x. Then it will
cancel with the 2x term in the second equation:

{{{system(matrix(2,5, -2x,""+"",8y,""="",132,

2x,""+"",y,""="",12))}}}
------------------------------
{{{system(matrix(1,11,"","","","","","","",9y,""="","",144))}}}
      {{{y}}}{{{""=""}}}{{{144/9}}}
      {{{y}}}{{{""=""}}}{{{16}}} 

Finish by subtituting 16 for y in any of the above equations
which contain both letters.  I'll pick this one

{{{matrix(1,5,2x,""+"",y,""="",12))}}}
{{{matrix(1,5,2x,""+"",16,""="",12))}}}
{{{matrix(1,5,"","",2x,""="",-4))}}}
{{{matrix(1,5,"","",x,""="",(-4)/2))}}}
{{{matrix(1,5,"","",x,""="",-2))}}}

The solution is (x,y) = (-2,16)

Edwin</pre>