For a determined product you can buy 12Kg for $8.39. To determine how much 1Kg of said product costs, you can apply cross multiplication to calculate it:
If 12 Kg cost $8.39
1 Kg costs $x:
[tex]\begin{gathered} \frac{8.39}{12}=\frac{x}{1} \\ \frac{8.39}{12}=x \\ x=0.699\cong0.70 \end{gathered}[/tex]The cost is $0.70/Kg