To find the highlighted partial product of 18 in Koda's area model for the multiplication \( 13 \times 16 \), we look at the individual components of the area model.
The grid represents the multiplication in terms of its parts:
- The top left box (10 × 10) represents \( 100 \),
- The top right box (10 × 6) represents \( 60 \),
- The bottom left box (3 × 10) represents \( 30 \),
- The bottom right box (3 × 6) represents \( 18 \).
The highlighted partial product of \( 18 \) corresponds to the calculation \( 3 \times 6 \).
Therefore, Koda made the calculation 3 × 6 to get the highlighted partial product.