A particular rock drill has a capital cost of $1.2 million dollars and will generate $350,000 of additional annual revenue after costs and taxes for the foreseeable future. What is the payback period for this investment, given an interest rate of 10%?

Enter your answer as decimal between the years where the payback period occurs. For example, if the payback period occurs anytime between years 11 and 12, you may enter "11.5"