For the project with net cash flows (excluding abandonment costs) as shown below, abandonment and decommissioning was originally at the end of year 13. Now, after discussions with the host government, we are offered the option to abandon any time between the end-of-year 10 and the end-of-year 13. If our company's discount rate is 10% and the cost of decommissioning is $100 million, when is the optimal time of abandonment?