To find the unit rate of stamps per sheet, you divide the total number of stamps by the number of sheets.
Given:
- Total stamps = 90
- Total sheets = 5
Now, calculate the unit rate:
\[ \text{Stamps per sheet} = \frac{90 \text{ stamps}}{5 \text{ sheets}} = 18 \text{ stamps per sheet} \]
So, the unit rate is 18 stamps per sheet.