You are considering investing in a new gold mine in South Africa. Gold in South Africa is buried very deep, so the mine will require an initial investment of $250 million. Once this investment is made, the mine is expected to produce revenues of $30 million per year for the next 20 years. It will cost $10 million per year to operate the mine. After 20 years, the gold will be depleted. The mine must then be stabilized on an ongoing basis, which will cost $5 million per year in perpetuity. Calculate the IRR of this investment. Plot the NPV as a function of the discount rate.)