<PRE><B>Question 435251</B>
Let {{{x}}} = pounds of $9/lb coffee to be added
{{{ 9x }}} = cost of coffee to be added
{{{ 3*30 = 90 }}} = cost of $3/lb coffee 
{{{ 7*(30 + x) }}} = cost of final mixture
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{{{ 9x + 90 = 7*(30 + x) }}}
{{{ 9x + 90 = 210 + 7x }}}
{{{ 2x = 210 - 90 }}}
{{{ 2x = 120 }}}
{{{ x = 60 }}}
60 pounds of $9/lb coffee must be added be added</PRE>