Question 575957
Let {{{ x }}} = pounds of $8/lb coffee needed
{{{ 8x }}} = cost of the $8/lb coffee 
{{{ 4*20 = 80 }}} = cost of the $4/lb coffee used
------------
{{{ ( 8x + 80 ) / ( x + 20 ) = 5 }}}
{{{ 8x + 80 = 5*( x + 20 ) }}}
{{{ 8x + 80 = 5x + 100 }}}
{{{ 3x = 20 }}}
{{{ x = 6.667 }}}
6 and 2/3 pounds of $8/lb coffee is needed
This makes {{{ 6.667 + 20 = 26.667 }}}
There is 26 and 2/3 pounds of the $5 /lb coffee to sell
check:
{{{ ( 8x + 80 ) / ( x + 20 ) = 5 }}}
{{{ ( 8*6.667 + 80 ) / ( 6.667 + 20 ) = 5 }}}
{{{ ( 53.333 + 80 ) / ( 26.667 ) = 5 }}}
{{{ 133.333 = 5*26.667 }}}
{{{ 133.333 = 133.333 }}}
OK