<s>[INST] The pod at departure point is empty. It is expected that a rider will drop off the pod for every 2 new riders that enter the pod. Thus, it takes $\frac{1}{3}$ of a mile for a rider to enter the pod, and $\frac{2}{3}$ of a mile for a rider to exit. 
For every 10 miles traveled, the pod earns $4. How much money can the pod earn per mile on average?[/INST]