First, we need to draw both points on the plane along with the line that crosses them, as follows:
Then, let's check whether those rates are proportional.
[tex]\begin{gathered} \frac{6}{3}=2 \\ \frac{9}{6}=\frac{3}{2}=1.5 \end{gathered}[/tex]
Then, each pound costs $2 and $1.5 in store B and C, respectively.
Therefore:
[tex]\begin{gathered} \text{rate of B}=\frac{2}{1.5}\text{ rate of C} \\ \Rightarrow\text{rate of B=}\frac{4}{3}\text{ rate of C} \end{gathered}[/tex]
Then, both rates are proportional, and the constant that defines the proportion is 4/3.
