Answer:
Option B is the correct answer.
Explanation:
Current number of butterflies in the park = 20 thousand.
Rate of increase of butterfly population = 4% = 0.04
The population of butterfly after 1 year = 20+0.04*20 = 20*1.04
The population of butterfly after 2 years = 20*1.04 + 20*1.04*0.04 = 20*1.04*1.04
The population of butterfly after 3 years = 20*1.04*1.04 + 20*1.04*1.04*0.04 = 20*1.04*1.04*1.04
So, population of butterfly after n years = 20*(1.04*1.04*1.04* .... n times)

Option B is the correct answer.
Answer:
Simple Interest: A = P(1+rt)
Step-by-step explanation:
P: the principal, the amount invested
A: the new balance
t: the time
r: the rate, (in decimal form)
Ex1: If $1000 is invested now with a simple interest of 8% per year. Find the new amount after two years.
P = $1000, t = 2 years, r = 0.08.
A = 1000(1+0.08(2)) = 1000(1.16) = 1160
D. 2 radians
Remember that: Radian=arc length/radius
In your case you have
arc length=2r
radius=r
so Radian=2r/r=2