Answer:
Option A. 4 radians
Step-by-step explanation:
step 1
Find the circumference of the circle
The circumference is equal to

we have

substitute


step 2
Find the measure of angle 
we know that
The circumference of the circle subtends a central angle of 2π radians
so
using proportion
Find out the central angle by an arc length of 20 cm

Answer:
The answer to your problem is the last option
Answer:
64.5%
Step-by-step explanation:
Initial amount N° = ?
Remaining amount after decay = N = ?
k = decay constant = 0.00012 
t = time = 3650 year
fraction remaining will be N/N°
From the decay equation, N = N°
N/N° = 
N/N° = 
N/N° = 
N/N° = 0.645 = 64.5%