For this case we have an equation of the form:

Where,
A: initial amount
b: growth rate
t: time in years.
Substituting values we have:

By the time the population is triple we have:

Rewriting we have:

Clearing t we have:
Answer:
It will take for the population to triple about:
t = 73 years
Well first of all if I had a multiplication question such as 12,000×1000 of course you would know it would be 12,000 well you would always use your place value chart saying ones tens hundreds thousands and thousands and hundreds
21√$42.84 ≈ 21√42.84=137.449773
Hope this helps~!