Final answer:
Based on the relationship between a star's mass and its main-sequence lifetime and the information provided in the table, a star with 20 times the mass of our Sun would likely have a lifespan of 30 billion years.
Step-by-step explanation:
The main-sequence lifetime of a star is directly proportional to its mass and inversely proportional to its rate of fuel consumption (luminosity). Based on this relationship, a star with 20 times the mass of our Sun would have a shorter lifespan compared to the Sun. The table provided indicates that the most massive stars spend only a few million years on the main sequence. Therefore, option 1) 10 billion years is unlikely. Option 2) 20 billion years is also unlikely. On the other hand, option 4) 40 billion years seems too long. So, the most likely lifespan for a star with 20 times the mass of our Sun would be option 3) 30 billion years.