Part A
Recall that unit rates is the amount of change in the dependent variable (y) over 1 increment of the independent variable (x). This is usually a ratio or a fraction.
In this case, the cost and the number of ounces are the dependent and independent variables respectively.
So, the unit rates, starting from the leftmost side of the array, are,
[tex]\dfrac{4.32 \:dollars}{9 \: oz} =0.48 \frac{dollar}{oz}[/tex] [tex]\dfrac{3 \: dollars}{5 \: oz}=0.6\frac{dollar}{oz}[/tex]
[tex]\dfrac{8.25\: dollars}{15\: oz} =0.55\frac{dollars}{oz}[/tex] [tex]\dfrac{3.22\: dollars}{7\:oz}=0.46\frac{dollars}{oz}[/tex]
Part B
Notice the measurements in each unit rate: it's in dollars per ounces. This tells us how much each ounce of popcorn cost.
Part C
The best package is the one with the cheapest rate, which is seen in package D or the one selling 7 ounces of popcorn for $3.22 at a rate of 0.46 dollars per oz (46¢ per oz).