To find the unit rate of stretch in millimeters per gram, you would need to have the specific values of the spring's stretch (in mm) for a given weight (in grams). The unit rate is calculated by dividing the stretch by the weight:
\[ \text{Unit rate} = \frac{\text{Stretch in mm}}{\text{Weight in grams}} \]
If you can provide the specific values from the image or describe them, I can help you calculate the unit rate.