Question 372841
It helps to get all the terminology straight,
otherwise, you can't talk about it
You have:
1st equation:
(term 1) + (term 2) = (term 3)
2nd equation:
(term 1) + (term 2) = (term 3)
What you are trying to do is 
get either the (term 1)'s equal to each other
or the (term 2)'s equal to each other.
Then the next step is to multiply both sides 
of equation 2 by -1

Then when add the equations, you get:
1st equation:
(term 1) + (term 2) = (term 3)
2nd equation:
-(term 1) - (term 2) = -(term 3) 
So, you've gotten rid of either the (term 1)'s or the (term 2)'s
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How do you get (term 1)'s equal to each other?
{{{3x + 11y = 34.5}}} 
{{{9x - 7y = -16.5}}}
Multiply both sides of equation 1 by {{{3}}}
{{{9x + 33y = 103.5}}}
Now you can multiply both sides of equation 2 by {{{-1}}}
and add the equations
{{{9x + 33y = 103.5}}}
{{{-9x + 7y = 16.5}}} (note that all the signs are changed)
Adding:
{{{40y = 120}}}
Divide both sides by {{{40}}}
{{{y = 3}}}
Now you can plug this result back into
either equation and find {{{x}}}
Does this help?