You are managing a production line in a factory producing plastic parts for a car. The lines injection molding machine is old and slow you estimate that a new machine could increase the sales revenue by 30,000 per year but the new machine would cost 150000. You propose the investment to the factorys financial department, and they tell you they can approve the investment only if the return is at least 12%. If both the old equipment to be replace and the new equipment have no salvage value, what is the minimum useful life the machine must have to be approved for the investment?