3/4 feet
You can set this up as an equation and solve

If you reflect across the x-axis, the y value change from positive to negative.
If you reflect across the y-axis, the x value changes from positive to negative
Both is a good deal. But the better deal is 10 liters for 24 dollars. Because there is more. Although 1 liter costs 2 dollars and 40 for both deals.
7.1(10) = 71 <== 10 times greater means multiply