Question 1002823
{{{ 2x + 13 = 3 }}}
You want to get {{{ x }}} alone on the left side and
what it is equal to on the right side.
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First, subtract {{{ 13 }}} from both sides
( if you do something to one side, you must do the same 
thing to the other side )
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{{{ 2x + 13 - 13 = 3 - 13 }}}
{{{ 2x = -10 }}}
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Divide both sides by {{{ 2 }}}
{{{ (2x)/2 = -10/2 }}}
{{{ x = -5 }}}
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Now check the answer by plugging it back into 
the original equation
{{{ 2x + 13 = 3 }}}
{{{ 2*(-5) + 13 = 3 }}}
{{{ -10 + 13 = 3 }}}
{{{ 3 = 3 }}}
OK
Hope this helps