The answer to your question is 2 5/27
Exponents can make the problem smaller and look less confusing. If you see a problem with 5*5*5*5*5*5*5*5 then you're going to eventually loose count and will have to keep repeating. But if you put 5 to the 8th power then you know right away just to multiply 5, (8) times,
A postulate is a statement in math that is so obvious that it does not need to be proven, that is basically what it means, in layman's terms
After the first 18 years, the population of 1500 will be doubled to 3000.
After the next 18 years, making 36 years total, the population of 3000 will double to 6000.
Your answer is 1 and 7/8.