<u>ANSWER</u>

<u>EXPLANATION</u>
The given series

This is an arithmetic series with a common difference of

The first term of the series is:

The general term is given by:




The last term is 81
We can use this to determine the number of terms in the series.




The summation notation is:

5% of 11 is 0.55. What number times 0.55 = 11? Well if we divide 11 by 0.55, we see that the answer is 20. So, the population will double in 20 years. If the population is 22 in 20, it stands to reason that it will take another 20 years to double from 22 to 44. So, the population will reach 44 in 40 years.
Hope this helps.
Hello from MrBillDoesMath!
Answer:
l = s/3.14 - r^2
Discussion:
s = 3.14 l + 3.14 r^2 => divide both sides by 3.14
s/3.14 = l + r^2 => subtract r^2 from both sides
(s/3.14) - r^2 = l
Thank you,
MrB