To find out how long it took Carla to run one mile, you can divide the total time by the total distance.
Carla took 36 minutes to run 4 miles.
To find the time taken for one mile: \[ \text{Time per mile} = \frac{\text{Total time}}{\text{Total distance}} = \frac{36 \text{ minutes}}{4 \text{ miles}} = 9 \text{ minutes/mile} \]
So, the correct response is: 9 minutes/mile.