[tex]\bf \begin{array}{lccclll}
&\stackrel{lb}{amount}&\stackrel{lb}{price}&\stackrel{total}{price}\\
&------&------&------\\
\textit{6 per lb coffee}&x&6&6x\\
\textit{3.5 per lb coffee}&y&3.5&3.5y\\
-------&------&------&------\\
mixture&25&5.25&131.25
\end{array}[/tex]
same as before, we add the 1st and 3rd columns, since the mixture is just the sum of the elements above it.
[tex]\bf \begin{cases}
x+y=25\implies \boxed{y}=25-x\\
6x+3.5y=131.25\\
----------\\
6x+3.5\left( \boxed{25-x} \right)=131.25
\end{cases}
\\\\\\
6x+87.5-3.5x=131.25\implies 2.5x=131.25-87.5
\\\\\\
2.5x=43.75\implies x=\cfrac{43.75}{2.5}\implies x=17.5[/tex]
how many lbs will it be of the 3.50 per lb coffee? well, y = 25 -x.
