6. A Japanese steel manufacturer is considering expanding operations. From experience, it estimates that new capacity additions obey the law F(y)=.00345y51, where the cost f(y) is measured in millions of dollars and y is measured in tons of steel produced. If the demand for steel is assumed to grow at the constant rate of 8,000 tons per year and future costs are discounted using a 10 percent discount rate, what is the optimal number of years between new plant openings