Suppose that an astronomer claims that there are currently 100 civilisations in the Milky Way galaxy that are technologically capable of communicating with us here on Earth. Using our galaxy's size, that would mean that the nearest such civilisation would be about 7500 light years away. The Milky Way star formation rate is about 6.50 per year, the percentage of stars with planets is approximately 100%, the number of planets per star that host earth-like planets could be about 0.100. Assuming that the percentage of earth-like planets that have life, that the percentage of those planets develop intelligent life, and that the percentage of planets with intelligent life that eventually can communicate across the galaxy are each 100%, we can calculate the average lifetime of these civilisations. a) [3] Determine this average lifetime, assuming the values in the paragraph above. b) [2] If we received a communication from such a civilisation here on Earth, explain whether or not the civilisation would be likely to still exist.