Answer: The correct answer is NP * FL * FC
Step-by-step explanation:
NP = The number of planets in our galaxy that are capable of sustaining any form of life
FL = The probability that life will eventually develop and spawn on an inhabitable planet
FC = The probability that a planet that has life will eventually evolve and develop the technology to build interstellar communication capabilities
Then our formula to support this possibility is NP * FL * FC
For example, if you have 500 planets in our galaxy that could support life with the probability that 1 in 5 could spawn life and of those 1 in 5 that could develop communications:
500 * 1/5 * 1/5 = 20 possible planets could meet this criteria