Question 996242
The break even point is at:
[ cost ] = [ cash received ]
Let {{{ n }}} = number of sold
cost = {{{ 40 + .25n }}}
cash received = {{{ .75n }}}
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{{{ 40 + .25n = .75n }}}
{{{ .5n = 40 }}}
{{{ n = 80 }}}
They must sell 80 cups to break even.
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Note that this problem assumes that 
they don't buy more juice than they
actually sell. If they bought 10 more cups
than they sold, then the left side would
look like: {{{ 40 + .25*( n + 10 ) }}}
Just thought I'd mention it.