Question 1052415
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Instead of doing yours for you, I will change the numbers,
do it step by step.  Then you can use it as a model to do 
yours exactly the same way step by step:
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4x + 5y = 21
{ y = -3x + 4
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Write 
4x + 5y = 21

Take out the y and put in (-3x + 4) in place of it

4x + 5(-3x + 4) = 21

Remove the parentheses by distributing the "+ 5" times
the "-3x", getting "- 15x" and also multiplying the "+ 5"
times the "+ 4" getting "+ 20", so write "- 15x + 20"
in place of + 5(-3x + 4)

4x - 15x + 20 = 21

Combine the "4x - 15x" as -11x, so write -11x instead of 
"4x - 15x":

    -11x + 20 = 21

Add - 20 to both sides:

 -11x + 20 - 20 = 21 - 20

The + 20 and the - 20 cancel out on the left,
so we just have -11x on the left. On the right
we replace the 21 - 20 by 1

          -11x = 1

We divide both sides by -11

         {{{(-11x)/(-11)}}}{{{""=""}}}{{{1/(-11)}}}

Then the -11's cancel, and the right side becomes {{{-1/11}}}.

So that means 

         {{{x}}}{{{""=""}}}{{{-1/11}}}

Now we take the original second equation:

         y = -3x + 4

And we substitute {{{(-1/11)}}} for x

         y = -3{{{(-1/11)}}} + 4

Multiply the -3 by the {{{(-1/11)}}}, getting {{{3/11}}}

         y = {{{3/11}}} + 4

Get the least common denominator which is 11 by multiplying
the +4 by {{{(11/11)}}} which just amounts to multiplying by 1:

         y = {{{3/11}}} + 4{{{(11/11)}}}

So we have

         y = {{{3/11}}} + {{{44/11}}}

or

         y = {{{47/11}}}

So the solution is (x,y) = {{{(matrix(1,3,-1/11,",",47/11))}}}

Now do yours exactly the same way.

Edwin</pre></b>