To find the unit rate of how long it took Carla to run 1 mile, we can divide the total time by the total distance.
Carla took 36 minutes to run 4 miles. To find the time per mile, we use the formula:
\[ \text{Time per mile} = \frac{\text{Total time}}{\text{Total distance}} = \frac{36 \text{ minutes}}{4 \text{ miles}} = 9 \text{ minutes per mile} \]
So, it took Carla 9 minutes to run 1 mile.