Question 1027413
{{{X}}} is the cost of 1 lb of butter
{{{Y}}} is the cost of 1 lb of peanuts
.
.
.

{{{12X+10Y=91}}} <--- Total cost
{{{Y=4X}}} <--- Cost comparison
Substituting,
{{{12X+10(4X)=91}}}
{{{12X+40X=91}}}
{{{52X=91}}}
{{{X=1.75}}}<--- Cost of 1 lb of butter