Question 708675
x and y, milk and beef quantities, in that order.
Prices today according to the discount: $3.10/gallon milk, 0.8(3)=$2.4/pound beef.


As a reminder, the units of milk is gallons and for beef is pounds.
Want to spend no more than $20 for this day.
{{{3.1x+2.4y<=20}}}


More comfortable in slope-intercept form, but as long as that there is in standard, you can quickly find x and y intercepts.  anyway,...
2.4y<=-3.1x+20
y<=-(3.1/2.4)x+20/2.4
{{{highlight(y<=-1.292x+8&1/3)}}}


Also, not if y=0, then x=6.45 "gallons" of milk.  No buying more than 6 gallons & 1 quart of milk today, for practical purposes.  Things change a bit if you are allowed to buy pints.  

{{{graph(300,300,0,10,0,10,-1.292*x+8.333)}}}

As example using this graph, you could buy 6 gallons of milk or less, and half a pound of beef or less, and that should cost less than or up to $20.
The region between the axes and the line are valid for "todays" discount prices.