To find the unit rate, you need to divide the total number of stamps by the number of sheets.
You have 12 stamps on 2 sheets.
To find the number of stamps per sheet, use the following calculation:
\[ \text{Stamps per sheet} = \frac{\text{Total number of stamps}}{\text{Number of sheets}} = \frac{12}{2} = 6 \]
Therefore, the unit rate is 6 stamps per sheet.