Question 320346
Check your first equation. 
There is no "=" sign.
I'm assuming it's {{{6x+5y=18}}}
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1.{{{6x+5y=18}}}
2.{{{x=28-5y}}}
Substitute eq. 2 directly into eq. 1,
{{{6(28-5y)+5y=18}}}
{{{168-30y+5y=18}}}
{{{-25y=-150}}}
{{{highlight( y=6)}}}
Then from eq. 2,
{{{x=28-5(6)}}}
{{{x=28-30}}}
{{{highlight( x=-2)}}}