Channel Tunnel Inc. plans to build an additional 23-mile-long tunnel under the English Channel for added train service. The cost (NINV) of the tunnel is expected to be $3.9 billion. Net cash inflows are expected to equal $817 million per year. How many years must the firm generate this cash inflow stream for investors to earn their required 20 percent rate of return? Use Table IV to answer the question. Round your answer to the nearest whole number. years