To find the unit rate when the stretch of a spring is proportional to the weight attached to it, we can express the relationship mathematically. If we let \( S \) represent the stretch of the spring in millimeters and \( W \) represent the weight attached to the spring in grams, then we can express the relationship as:
\[ S = kW \]
where \( k \) is the constant of proportionality (the unit rate).
To find the unit rate \( k \), you would typically need specific values for \( S \) and \( W \). If you know a specific stretch of the spring for a given weight, you can calculate the unit rate as follows:
\[ k = \frac{S}{W} \]
This will give you the stretch per gram, expressed in millimeters per gram.
For example, if a weight of 200 grams stretches the spring 50 millimeters, the calculation for the unit rate would be:
\[ k = \frac{50 \text{ mm}}{200 \text{ grams}} = 0.25 \text{ mm/gram} \]
If you provide specific values for the stretch and the weight, I can help calculate the exact unit rate.