Suppose that during a recent 35-year period, there were four volcanic eruptions sufficiently powerful to reduce the amount of power generated by solar panels by at least 15% for a period of a year. Call these "Class D15" volcanoes. Suppose that the return on investment from installing solar panels is often calculated over a 20-year period. What is the probability that, during a 20-year period, there will be two or more "Class D15" volcanic eruptions?