Given:
The number of whole pies, x=6.
The number of whole cakes, y=4.
Each pie is cut into 1/3 slices.
So, the number of slices of pies obtained after cutting one pie is,
![n=\frac{1\text{ }}{(1)/(3)\text{ }}=3](https://img.qammunity.org/2023/formulas/mathematics/college/r0asl1kl9i8yg1sbr9u32p6hqeei1xegdu.png)
Now, the number of slices of pie made by cutting x=6 whole pies is,
![\begin{gathered} N=nx \\ =3*6 \\ =18 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/nqbfu04enzxv4t445vak3lz7fq782pnrbm.png)
Therefore, Justin made 18 slices of pies.
Hence, option D is correct.
![(1)/(3)+(1)/(3)+(1)/(3)=(1)/(3)*3=1](https://img.qammunity.org/2023/formulas/mathematics/college/66l6pekkrovenj5xx3lfhnzf9giuwa65pd.png)