To find the density of a substance, you can use the formula:
\[ \text{Density} = \frac{\text{Mass}}{\text{Volume}} \]
In this case, you have a mass of 170 grams and a volume of 9 cm³.
Now, substituting the values into the formula:
\[ \text{Density} = \frac{170 \text{ g}}{9 \text{ cm}^3} \approx 18.89 \text{ g/cm}^3 \]
When rounding to one decimal place, this is approximately 18.9 g/cm³. Therefore, the closest answer from the options provided is:
D) 18.8 g/cm³