To find the unit rate of plants per row, you divide the total number of plants by the number of rows.
Given:
- Total plants = 189
- Total rows = 9
The calculation is:
\[ \text{Plants per row} = \frac{189 \text{ plants}}{9 \text{ rows}} = 21 \text{ plants per row} \]
So, there are 21 plants per row.